Question 1009815
I think you missed part of the problem setup.
" In 15 years, Stephanie will be five times as old as Kate 2 years ago "
This would be:
{{{ S + 15 = 5*( K - 2 ) }}}
{{{ S + 15 = 5K - 10 }}}
{{{ S = 5K - 25 }}}
------------------
You already have:
{{{ S = 4K - 15 }}} ,so
{{{ 5K - 25 = 4K - 15 }}}
{{{ K = 10 }}}
and
{{{ S = 5K - 25 }}}
{{{ S = 5*10 - 25 }}}
{{{ S = 50 - 25 }}}
{{{ S = 25 }}}
Kate is 10 and Stephanie is 25 
Hope I got it