Sally is 54 years old, and her mother is 80. How many years ago was Sally’s mother three times her age?
So you can give x=1/3. And so sally 54-x is what Sally’s age was.
41 years ago Sally was 13 and her mother was 39.
I will make it X years ago
\(80-X=3(54-X)\\ 80-X=162-3X\\ 80-X+3X=162-3X+3X\\ 80+2X=162\\ 2X=82\\ X=41 \)
So it was 41 years ago, just like guest said :)