Question

The square of Mark's age 3 years ago is 6 times the age he will be in 9 years. What is his age now?

15
12
9

Answer 1

15

Explanation:

((x-3)^2) / 6 = x + 9

Multiply both sides by 6.

6x + 54 = ((x-3)^2)

Expand.

6x + 54 = x^2 - 6x + 9

Simplify.

x^2 - 12x - 45 = 0

Solve using quadratic formula.

x = 15, -3

Since ages can only be positive, the answer is 15 years old.