Let the man's age be M, and the son's, S
Then we get: M - 4 = 6(S - 4)_____M - 4 = 6S - 24_____M = 6S - 20 ------- eq (i)
Also, M + 12 = 2(S + 12)_____M + 12 = 2S + 24_____M = 2S + 12 ------ eq (ii)
6S - 20 = 2S + 12 ------ Equating the two M values
6S - 2S = 12 + 20
4S = 32