Google combo chart percentage line error shows down

public partial class student_master : System.Web.UI.Page
{
mydb db = new mydb();
string st = "";
//SqlCommand cm;
SqlDataReader dr;
double x = 0;
double fmax_marks, smax_marks;
protected void Page_Load(object sender, EventArgs e)
{

if (!IsPostBack)
{
BindGvdata();
BindChart();
}
}
private void BindGvdata()
{
gvdata.DataSource = GetChartData();
gvdata.DataBind();
}
private void BindChart()
{
DataTable dschartdata = new DataTable();
StringBuilder strScript = new StringBuilder();
try
{
dschartdata = GetChartData();
strScript.Append(@"
");

ltScripts.Text = strScript.ToString();
}
catch
{ }
finally
{
dschartdata.Dispose();
strScript.Clear();

}
}

private DataTable GetChartData()
{
DataSet dsData = new DataSet();
try
{
SqlConnection dd = new SqlConnection(WebConfigurationManager.AppSettings["con"]);


st = @"SELECT MAX(exam_details.max_marks) AS max_marks
FROM exam_master INNER JOIN exam_details ON exam_master.e_id = exam_details.e_id
WHERE (exam_master.c_id = 1) AND (exam_master.e_name LIKE 'FA%')";
dr = db.readall(st);

if (dr.Read() == true)
{
fmax_marks = Convert.ToDouble(dr[0].ToString());
}

st = @"SELECT MAX(exam_details.max_marks) AS max_marks
FROM exam_master INNER JOIN exam_details ON exam_master.e_id = exam_details.e_id
WHERE (exam_master.c_id = 1) AND (exam_master.e_name LIKE 'SA%')";
dr = db.readall(st);
if (dr.Read() == true)
{
smax_marks = Convert.ToDouble(dr[0].ToString());
}

st = @" SELECT results.sb_id, student_master.s_name, results.FA1 / " + fmax_marks + " *100 AS FA1, results.FA1 / " + fmax_marks + "* 100 AS FA2, results.SA1 / " + smax_marks + " * 100 AS SA1, results.FA1 / " + fmax_marks + "*100 AS FA3, results.FA1 / " + fmax_marks + " * 100 AS FA4, results.SA2 / " + smax_marks + " * 100 AS SA2, results.st_no, subject_master.sub_name,0 as '%'";
st += " FROM results INNER JOIN student_master ON results.st_no = student_master.st_no INNER JOIN subject_master ON results.sb_id = subject_master.sb_id WHERE (results.st_no = 1) AND (results.c_id = 1)";
dd.Open();
db.fids(st, gvdata);

SqlDataAdapter sqlda = new SqlDataAdapter(st, dd);
sqlda.Fill(dsData);
dd.Close();
}
catch
{
throw;
}
return dsData.Tables[0];


}

protected void gvdata_RowDataBound(object sender, GridViewRowEventArgs e)
{
//if (e.Row.RowType == DataControlRowType.DataRow)
//{

foreach(GridViewRow row in gvdata.Rows)
{
// Label label2 = (Label)row.FindControl("label");
Label label3 = (Label)row.FindControl("Label3");
Label label4 = (Label)row.FindControl("Label4");
Label label5 = (Label)row.FindControl("Label5");
Label label6 = (Label)row.FindControl("Label6");
Label label7 = (Label)row.FindControl("Label7");
Label label8 = (Label)row.FindControl("Label8");
Label label1 = (Label)row.FindControl("Label1");

// st = @" SELECT id ,sum(FA1+FA2+SA1+FA3+FA4+SA2 ) as total, sum(FA1+FA2+SA1+FA3+FA4+SA2 )/6 as avg from results group by id";
x = (Convert.ToDouble(db.chk_ch_0(label3.Text)) + Convert.ToDouble(db.chk_ch_0(label4.Text)) + Convert.ToDouble(db.chk_ch_0(label5.Text)) + Convert.ToDouble(db.chk_ch_0(label6.Text)) + Convert.ToDouble(db.chk_ch_0(label7.Text)) + Convert.ToDouble(db.chk_ch_0(label8.Text))) / 6;

// st = (db.chk_ch_0(label3.Text) + db.chk_ch_0(label4.Text) + db.chk_ch_0(label5.Text) + db.chk_ch_0(label6.Text) + db.chk_ch_0(label7.Text) + db.chk_ch_0(label8.Text));
label1.Text = x.ToString();
}


// }

}