Answer:
Coupon B
Step-by-step explanation:
Given



Required
Which coupon is better
From the question, we have:


Coupon B means that:



By comparison:
Coupon B gives him a better buy because: 
P + 10 = 20 Subtract 10 from both sides
P = 10
Substitute P = 10 into P + Q = 16
P + Q = 16 Plug in 10 for P
10 + Q = 16 Subtract 10 from both sides
Q = 6