simple marksheet program in c#

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C#

i want to make a form that contain 5 text box.
for first 4 text boxes take input. and the textbox 5 shows the result.
conditions:
the form contains 3 buttons:
1. it shows the total of marks obtain.
2. it shows the percentage of marks obtain but if the number input in any text box is less than 33 it shows fail
3. it shows the grade:
if total>=60 print a; if total>=45 print b; if total>=33 print c else fail; but it number obtain in any subject is less than 33 it also shows fail.