Problem solving using algebra and equations

Question

Today, A is six times as old as B. In 15 years time, A will be three times as old as B. Find how old A will be in 9 years time.

Answer 1

A = 6b

A+15 = 3(b+15)

6b + 15 = 3b + 45

3b + 15 = 45

3b = 30

b = 10

A = 60