So I have this riddle and I need help and it goes like this:

When I was 6
My sister was half my age
Now I’m 70.
How old is my sister?

3 answers

When I was 6
My sister was half my age

How old was your sister then?

How much younger than you was she?

How much younger than you is she now?
6/2 = 3

Take it from there.
Actually this isn't a riddle. It is a math problem.