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The perimeter of a rectangle can be determined by adding the four sides together. The sum of the shorter sides is $x+x,$ and the sum of the longer sides is $(x+7)$ + $(x+7).$ If these are added, we'll get the perimeter of the rectangle.

$x+x+(x+7)+(x+7)$

RemoveParRemove parentheses

$x+x+x+7+x+7$

CommutativePropAddCommutative Property of Addition

$x+x+x+x+7+7$

AddTermsAdd terms

$4x+14$

b