Find the current age

In 15 years, a child's age will be 9 years less than four times her current age.  Find her current age. 

x = child's age now
x + 15 = child's age in 15 years 

x + 15 = 4x - 9 {in 15 years she will be 9 less than 4 times her age now}
15 = 3x - 9 {subtracted x from each side}
24 = 3x {added 9 to each side}
x = 8 {divided each side by 3} 

her current age is 8

- Algebra House