Question 697873
Set-Up
--------------
L = length
W = width
Equation 1: {{{84 = 2L + 2W}}}
Equation 2: {{{L = 2W - 3}}}

Solution:
--------------
Plug (2W - 3) into equation 1 for L
Equation 1: {{{84 = 2L + 2W}}}
{{{84 = 2*(2W - 3) + 2W}}}
Simplify
{{{84 = 4W - 6 + 2W}}}
Simplify
{{{84 = 6W - 6}}}
Add 6 to both sides
{{{90 = 6W}}}
Divide both sides by 6
{{{highlight(15 = W)}}}
Now plug 15 into equation 2 for W
Equation 2: {{{L = 2W - 3}}}
{{{L = 2*(15) - 3}}}
{{{L = 30 - 3}}}
{{{highlight_green(L = 27)}}}