Question 902467
p = 200 ft, perimeter
A = 1875 ft^2, area
x and y are the unknown dimensions.


2x+2y=p and xy=A
-
{{{2y=p-2x}}}
{{{y=p/2-x}}}
Substitute into A equation.
{{{x(p/2-x)=A}}}
{{{(p/2)x-x^2-A=0}}}
{{{-x^2+(p/2)x-A=0}}}
{{{highlight_green(x^2-(p/2)x+A=0)}}}
You may find that substituting the values now allows you to factor the quadratic expression; but this is not always the case.
{{{highlight(x=((p/2)+- sqrt((p/2)^2-4*A))/2)}}}


You might try to examine the expression for any other simplifications; or you could substitute the values (if not done already) and use the result for x to evaluate y.