#### Answer

H. $26$

#### Work Step by Step

The perimeter of a square is $P=4s$. With a side length of $2x$, the perimeter is $P=4(2x)=8x$. The perimeter of a triangle is the sum of the lengths of the sides. In this case, it is $P=3x+4x-3+16=7x+13$. Since the two perimeters are equal, we write an equation relating them: $7x+13=8x$. To solve for $x$, we simply subtract $7x$ from each side of the equation: $13=x$. Since the length of a side of the square is equal to $2x$, it is $2(13)=26$, which is choice H.