Question 443188
Let {{{s}}} = Sister's age
Let {{{m}}} = Max's age
given:
{{{ m = 4s }}}
{{{ s = m - 9 }}}
By substitution,
{{{ m = 4*(m - 9) }}}
{{{ m = 4m - 36 }}}
{{{ 3m = 36 }}}
{{{ m = 12 }}}
Max is 12
check:
{{{ s = m - 9 }}}
{{{ s = 3 }}}
and
{{{ m = 4s }}}
{{{ m = 4*3 }}}
{{{ m = 12 }}}
OK