Question 964638
The area of a rectangle is,
{{{A=L*W}}}
where L is length and W is the width.
One of the dimensions is x. 
Let x be the length (doesn't matter which you choose, the equation will work out the same).
The length of the wire is also equal to the perimeter of the rectangle,
{{{P=2(L+W)=30}}}
So,
{{{L+W=15}}}
{{{x+W=15}}}
{{{W=15-x}}}
So then substituting back into the area equation,
{{{A=x(15-x)}}}