If a + 3b = 13 and a + b = 5, the value of b is?

A. 1

B. 4.5

C. 7

D. 4

Ans: D

First, multiply a+b=5 by 3 to make it 3a+3b=15

Second, subtract this equation from a+3b=13 to give 2a=2

Therefore, a=1

Substitute this into a+3b=13, to give 1+3b=13

So, 3b=12

Divide this 3b=12 by 3 to get for.

Therefore, b=4

The value of b is 4

a=1

1+3 (4) = 13

1+4=5