Let x = the length of the morning commute and Y = the length of the back road, im miles. Then from the condition, you have these two equations Y + X = 57 ( her total commute distance ) Y - X = 7 ( back road is 7 miles longer than . . . ) Subtract the second equation from the first one. You will get 2X = 50; hence X = 50/2 = 25 miles. It is your answer.