62,66,70,74

In 8 years Mac's grandma will be twice as old as she was 29 years ago. How old will Mac's grandmother be in 4 years

Let her age now = A

29 years ago her age = A - 29

And in 8 years, her age will be A + 8

So...we know that

2 (A - 29) = A + 8         simplify

2A - 58 =  A + 8        add 58 to both sides, subtract A from both sides

A =  66       this is her age now

So....in 4 years, she will be   70

Let her age 29 years ago =A

A + 29 + 8 = 2A

A =37 - her age 29 years ago

37 + 29 + 8 - 4 =70 years 4 years from now.