Sharon is 42 years old. Her daughter is 12 years old. How many years ago was Sharon 4 times older than her daughter?

Sharon: 40

Daughter: 10

To do this, we need to know how much older than her daughter Sharon. She is 30 years older, so we get

d = s - 30

We want to figure out when d = s - 30, and 4d = s, so here's what we do:

Since 4d = s, we can substitute 4d for all occurences of s

d = 4d - 30

And then we can solve for d

-3d=-30

d=10

And then we plug that number into our original equation

10 = s-30

40 = s

Sharon was 40 years old when she was 4 times her daughter's age. Since she is now 42, we know she was 4 times her daughter's age 2 years ago