check the minimum value (Doube Data Type)

how can i check minimun value from 3 variable like this : MK_1 = 60, MK_2 = 50, MK_3 = 55

private void HitungNilaiKompre()

{

if (txtPenguji1_Nilai.Text.Trim().Length == 0) txtPenguji1_Nilai.Text = "0";

if (txtPenguji2_Nilai.Text.Trim().Length == 0) txtPenguji2_Nilai.Text = "0";

if (txtPenguji3_Nilai.Text.Trim().Length == 0) txtPenguji3_Nilai.Text = "0";

double NILAI_MK_1 = Convert.ToDouble(txtPenguji1_Nilai.Text);

double NILAI_MK_2 = Convert.ToDouble(txtPenguji2_Nilai.Text);

double NILAI_MK_3 = Convert.ToDouble(txtPenguji3_Nilai.Text);

double TOTAL = (NILAI_MK_1 + NILAI_MK_2 + NILAI_MK_3);

double RATA = ((NILAI_MK_1 + NILAI_MK_2 + NILAI_MK_3) / 3);

string MK_BERSYARAT = "";

string PENGUJI_BERSYARAT = "";

string hasil_akhir = "";

if (TOTAL >= 180)

{

hasil_akhir = "Lulus";

}

else if (TOTAL >= 162 && TOTAL < 180)

{

hasil_akhir = "Bersyarat";

if (NILAI_MK_1 < 60)

{

MK_BERSYARAT = tbMK_1.Text;

PENGUJI_BERSYARAT = cbPenguji_1.Text;

}

if (NILAI_MK_2 < 60)

{

MK_BERSYARAT = tbMK_2.Text;

PENGUJI_BERSYARAT = cbPenguji_2.Text;

}

if (NILAI_MK_3 < 60)

{

MK_BERSYARAT = tbMK_3.Text;

PENGUJI_BERSYARAT = cbPenguji_3.Text;

}

else if (TOTAL > 0 && TOTAL < 162)

{

hasil_akhir = "Tidak Lulus";

}

else

{

hasil_akhir = "Tidak Hadir";

}

txtRata.Text = RATA.ToString("N2");

txtHasil.Text = hasil_akhir;

txtMK_Bersyarat.Text = MK_BERSYARAT;

txtPenguji_Bersyarat.Text = PENGUJI_BERSYARAT;

}

the problem in 'bersyarat' if i insert : MK_1 = 60, MK_2 = 50, MK_3 = 55

why the minimum value is 55, i know the problem in here