Question 53900
Rectangles are four sided figures where the opposite sides are equal.  We find the perimeter of any polygon by adding the sides together.  Therefore the formula for the perimeter of a rectangle is:
Peremeter(P)=width(W)+width(W)+length(L)+length(L)
P=W+W+L+L
P=2W+2L
For the first problem:
P=64 m
Let width=x
The length is 4m longer, so let leght=x+4
Plug your values into the formula and solve for x:
64=2x+2(x+4)
64=2x+2x+8
64=4x+8
64-8=4x+8-8
56=4x
{{{56/4=4x/4}}}
{{{14=cross(4)x/cross(4)}}}
14=x
Width:x=14 m
Lenght:x+4=14+4=18m
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For the second one:
P=90
Width=x
Length=x+21
Problem:
90=2(x)+2(x+21)
90=2x+2x+42
90=4x+42
90-42=4x+42-42
48=4x
{{{48/4=4x/4}}}
{{{12=cross(4)x/cross(4)}}}
12=x
Width:x=12 ft.
Length:x+21=12+21=33 ft.
Happy Calculating!!!!