Question 75657
The perimeter of a rectangle is the width+length+width+length. Since the 2 width's   are the same we can say w+w=2w. The same thing applies for the length: L+L=2L. So the perimeter formula can be written as:

{{{P=2w+2L}}}    where P is the perimeter
{{{18=2(5)+2L}}}    Now plug in the given perimeter and the width to find the length
{{{18=10+2L}}}
{{{18-10=cross(10-10)+2L}}} Subtract 10 from both sides
{{{8=2L}}}
{{{8/2=cross(2/2)L}}} Divide both sides by 2
{{{L=4}}}
So the length is 4 feet
<p>
Check:
{{{18=2(5)+2(4)}}}
{{{18=10+8}}}
{{{18=18}}} works