A
Working:
Tan(angle)=opposite/adjacent
Tan60 = x/7root3
x=7root3 x Tan60
Enter in calculator
x=21
You have to go over then up (x,y)
Solution :
Let A = Economics, B = Mathematics
n(A) = 311, n(B) = 243, 
a). So, 
= 311 + 243 - 135
= 419
b). n(A only) = 311 - 135
= 176
n(B only) = 243 - 135
= 108
Exactly one of these two courses

= 0.568
c). Neither economics nor mathematics


= 0.162