Given
Rob is twice Joshua's age
Nick is 5 years older than Joshua.
sum of all their ages is 45.
Find the age of nick.
To proof
As given
Rob is twice Joshua's age
let Joshua's age = x
than Rob age = 2x
Nick is 5 years older than Joshua.
Nick age = 5 + x
sum of all their ages is 45
than the equation becomes
Joshua's age + Rob age + Nick age = 45
put the value
x + 2x + 5 + x = 45
4x = 40
x = 10
Joshua's age = 10 year
than Rob age = 20 year
Nick age = 5 + 10
= 15year
Hence proved