Question

four years hence a boy will be twice as old as he was 6 years ago. what is his present age?

Answer 1

Let his age now be "x":
Equation:
x+4 = 2(x-6)
x+4 = 2x-12
x = 16

Answer 2

let the present age of the boy be x,
hence, after four years boys age,
therefore,x+4=2×(x-6)
x+4=2x-12
x=16