how can update my column valu with add new vale in old value

Question

 

 i update Amount =  Amount +  txtAmut.Text

 how can do?????

 

if (con.State == ConnectionState.Closed)

con.Open();

string UpdateQuery = "UPDATE Student SET DueDate= '" + txtNewDat.Text + "' WHERE Admission_ID= " + labstuid.Text + Environment.NewLine +

"UPDATE FeeDeposit SET Amount= '" + txtAmut.Text + "' WHERE Admission_ID= " + labstuid.Text;

SqlCommand cmd1 = new SqlCommand(UpdateQuery,con);

cmd1.ExecuteNonQuery();