If we assume that Lisa is x years old, then Richard will be (x + 6)years
In 5 years time
Lisa = x +5 years
Richard = x +11 years
sum will be 2x + 16 years
4 years ago
Lisa = x-4 years
Richard = x + 2
Sum will be 2x - 2
Therefore;
2(2x-2) = 2x +16
4x -4 = 2x +16
2x = 20
x = 10
Thus, the present age of Lisa is 10 years and that of Richard is 16 years