Question 184327
let m="man now" and s="son now"


"A man will be three times as old as his son will be in nine years" ___ m+9=3(s+9)


"he is six times as old as his son is now" ___ m=6s


"how old is the SON?" ___ substituting ___ (6s)+9=3(s+9)


expanding ___ 6s+9=3s+27


subtracting 3s+9 ___ 3s=18


dividing by 3 ___ s=6