Explanation:
let jon age be x
dad age is 2 of x i.e 2x
grandpa age is 7 + 3(x)
The sum of jon dad and grandpa age is 145 i.e
x + 2x + (7+3x) = 145
3x +. 7 + 3x = 145
6x = 145- 7
6x = 138
divide both sides by 6
x = 23
jon age is 23
while
grandpa age is
7 + 3(x)
7 + 3(23)
7 + 69
76.