Question 1169682
s, son
m, man
man is four times older than son:  {{{m=s+4s=5s}}}



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 in four years time he will be three times as old .
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{{{m+4=3(s+4)}}}

Make the substitution for m;

{{{5s+4=3(s+4)}}}
finish to solve for s.  


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{{{5s+4=3s+12}}}
{{{2s=8}}}
{{{highlight(s=4)}}}----{{{highlight(m=5*4=20)}}}.


The man is 20 and the son is 4.