Question 869966
Let x = the number of years



If we subtract x from each age, we get



Sandra's age x yrs ago: 36 - x
Son's age x yrs ago:  14 - x



We want to know when she was 3 times older, so 



(Sandra's age x years ago) = 3*(Son's age x yrs ago)



36 - x = 3*(14 - x)



Now we solve for x



36 - x = 3*(14 - x)



36 - x = 3*(14) + 3*(-x)



36 - x = 42 - 3x



36 = 42 - 3x + x



36 - 42 = -3x + x



-6 = -2x



-6/(-2) = x



3 = x



x = 3



So <font color="red">3 years ago</font>, Sandra was 3 times older than her son (sandra = 33 years, son = 11 years)