Richard is 6 years older than Lisa, and in 5 years the sum of their ages will be twice as much as the sum of their ages 4 years ago. Find their present ages.
Lisa's present age --- x
Richard's present age --- x+6
5 years from now:
Lisa ---- x+5
Richard -- x+11
4 years ago:
Lisa --- x-4
Richard --- x+2
x+5 + x+11 = 2(x-4 + x+2)
2x + 16 = 4x - 4
20 = 2x
x = 10
Lisa is 10 and Richard is 16