Charles is four times as old as his daughter Nina.Eight years ago he was ten times as old as Nina. How old is Charles today?
My 1st "let" statement is usually associated with the variable that's being sought. In other words, here I would say, "Let Charles' age be C."
But, this would involve FRACTIONS, and that's a topic that most would rather stay away from, you included, I'd assume! So, I'll go with Nina.
Let Nina's age be N
Then Charles' is 4N
We then get: 4N - 8 = 10(N - 8)
4N - 8 = 10N - 80
4N - 40N = - 80 + 8
- 6N = - 72
N, or Nina's age is: 
Therefore, Charles is: 
