Ade was 4 times as old as his son 8 years ago. Ade will be twice as old as his son in 8 years time. What are their present ages?
4(s - 8) = A - 8 ... 4 s - 32 = A - 8
2(s + 8) = A + 8 ... 2 s + 16 = A + 8
subtracting (to eliminate A) ... 2 s - 48 = -16
solve for s , then substitute back to find A