So basically what each of these questions is asking you to do is put a number into the equation in place of the letter.
31:
13+34=47
32:
100/5=20
33:
657-298=359
34:
(5)(14)=70
35:
2(13)+34+3(5)=
26+34+3(5)=
26+34+15=75
36:
[(2.5^2)+1.75]3.2=
(6.25+1.75)3.2=
(8)3.2=25.6
Please remember to use PEMDAS! Hope that helped!