Question 898106
f and s


{{{f=3s}}}
and
{{{f-9=4(s-9)}}}


{{{f-9=4s-36}}}
{{{f=4s-36+9}}}
{{{f=4s-27}}}
Substitute
{{{3s=4s-27}}}
{{{-s=-27}}}
{{{highlight(s=27)}}}
-
{{{f=3*27}}}
{{{highlight(f=81)}}}