Answer
$24x+144$
Work Step by Step
Subtract the area of the blue square from the total area of the rug to find the area of the green band. The blue square has a side length of x. The rug has a side length of x+12.
Remember that the square of a binomial is the square of the first term, plus twice the product of the two terms, plus the square of the second term.
$(x+12)^2-x^2\longrightarrow$ square the binomial
=$x^2+24x+144-x^2\longrightarrow$ combine like terms
=$24x+144$
