Question 690520
Set-Up
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X = length
Y = width
Equation 1: {{{46 = 2X + 2Y}}}
Equation 2: {{{X = 2Y + 8}}}  That came from 2*(Y+4)

Solution:
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Plug (2Y + 8) into equation 1 for X
Equation 1: {{{46 = 2X + 2Y}}}
{{{46 = 2(2Y + 8) + 2Y}}} Simplify
{{{46 = 4Y + 16 + 2Y}}} Combine like terms
{{{46 = 6Y + 16}}} Subtract 16 from both sides
{{{30 = 6y}}} Divide both sides by 6
{{{highlight(5 = Y)}}}
Now plug 5 into equation 2 for Y
Equation 2: {{{X = 2Y + 8}}}
{{{X = 2*(5) + 8}}}
{{{highlight(X = 18)}}}