Given: After 15 years, the child will be three times as old as she was 3 years ago Calculation: Let the present age of the child be x. ⇒ Age of child, 3 years ago = x – 3 and Age of child after 15 years = x + 15 According to the question x+15=3×(x–3) ⇒ x+15=3x–9 ⇒ 2x=15+9=24 ⇒ x=12 years = present age of child