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.

Step-by-step explanation:

Let his age now be x years. Then:

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

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

x^2 - 12x - 45 = 0

(x - 15) (x + 3) = 0

x = 15, - 3

We ignore the negative so his age now is 15.

Age = 15

Step-by-step explanation:

Let a be for age at the moment

(a-3) ^2 = 6 (a+9)

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

a^2-12a-45

(a-15) (a+3)

a=15 or a=-3

Age cannot be negative (-)

Therefore

Age = 15