Answer
$4x^{2}+28x+49$
Work Step by Step
$\text{Length of a side of the square}=x+7+x=2x+7$
$\text{Area of the square}=(2x+7)^{2}$
Using square of a binomial pattern $(a+b)^{2}=a^{2}+2ab+b^{2}$, we have
$(2x+7)^{2}=(2x)^{2}+2(2x)(7)+7^{2}$
$=4x^{2}+28x+49$
