Question 214079
{{{A = x*y}}} cm2
{{{y = A/x}}}
{{{P = 35}}} cm
{{{P = 2x + 2y}}}
{{{2x + 2y = 35}}}
{{{2y = 35 - 2x}}}
{{{2*(A/x) = 35 - 2x}}}
{{{2A = 35x - 2x^2}}}
{{{A = -x^2 + 17.5x}}} answer
check answer:
Suppose {{{x = 12}}} cm
{{{A = -144 + 17.5*12}}}
{{{A = -144 + 210}}}
{{{A = 66}}} cm2 
{{{P = 2x + 2y}}}
{{{35 = 2*12 + 2y}}}
{{{2y = 35 - 24}}}
{{{2y = 11}}}
{{{y = 5.5}}}
{{{A = xy}}}
{{{A = 12*5.5}}}
{{{A = 66}}} cm2
OK