Question 615867
Okay, so we need to represent your age as an unknown. Let us say x.

Five years from now you are going to be x + 5

Eight years ago your mum was twice this i.e. 2(x+5) or 2x+10

It also gives a clue at how old your mum was 8 years ago in another way:
She was 27 + your age at the time and you would have been x-8. So this means she was:

27+x-8

As both formulas represent her age 8 years ago they are equal to each other so:

2x+10 = 27+x-8

Solve for x:

2x-x = 27-8-10
x=9

so you would be 9 years old.