Question 948193
{{{F=3S}}}
{{{F-12=6(S-12)}}}
{{{F-12=6S-72}}}
{{{F-6S=-60}}}
Substituting,
{{{3S-6S=-60}}}
{{{-3S=-60}}}
{{{S=20}}}
So then,
{{{F=3(20)}}}
{{{F=60}}}