ricky is now twice is old as he was 8 years ago: R = 2(R-8)

For this, Ricky is twice as old as (he was 8 years ago).

8 years ago he was R - 8
Twice that is 2(R - 8)

pic frame M is $10 less than 3 times the cost of pic frame N: M=3N-10

10 less than 3 times (the cost of the pic frame)

Notice that the 3 is multiplying JUST the cost, and then having 10 taken away from it. That results in 3N - 10.

3(N-10) would read "three times ten less than the cost"

great, thanks a lot!