Question 1074753
{{{S=F/2}}}
{{{F=2S}}}
and
{{{(S-10)*(F-10)=600}}}
Substituting,
{{{(S-10)(2S-10)=600}}}
{{{2S^2-30S+100=600}}}
{{{2S^2-30S-500=0}}}
{{{S^2-15S-250=0}}}
{{{(S-25)(S+10)=0}}}
Only positive solutions make sense here,
{{{S-25=0}}}
{{{S=25}}}
So then, 
{{{F=2(25)}}}
{{{F=50}}}