Question 932799
Let:

Present:
Michael - {{{17+x}}}
John - {{{x}}}

In 4 years:
Michael - {{{21+x}}}
John {{{4+x}}}

{{{(21+x)+(4+x)=49}}}
{{{2x+25=49}}}
{{{2x=24}}}
{{{x=12}}}

Michael's Present Age:
17+x
17+12
=29 years old 


Hope that helps! :*