Araba is 3 years younger means when you add 3 years to Araba's age, you will get the sister's age Let x= Araba's age The sister's age =x+3 Sum means addition. If the sum of their ages is 17 years means when you add their ages, you will get 17 Araba's age + Sister's age =17 x+x+3=17 2x=17−3 2x=14 Divide both sides by 2 x=