We will be needing the concept of quadratic equation to solve. Calculation: Let the present age of sister be x Present age of brother =x+7 Sister's age 5 years ago =x−5 Brother's age 5 years ago =x+2 ⇒(x−5)(x+2)=30 ⇒x2−3x−10=30 ⇒x2−3x−40=0 ⇒(x−8)(x+5)=0 ⇒x=8 ∴ Present age of brother =8+7=15 years