Arman is six times older than his sister. His sister is 2 years old four years ago. In how many years will Arman's age be 40? Let's be accurate as possible.
Arman's sister is 4 + 2 = 6 years old now. So, Arman is 6 x 6 = 36 years old. Hence, Arman will be 40 in 40 - 36 = 4 years.
The answer: 4.