the perimeter will be the outer border, and in this case we have three semi-circles and one square, well, the semi-circles have a diameter of 7, we can just get the circumference of all 3 semi-circles add them and append the 7 ft at the bottom, Check picture below.
[tex]\bf \textit{circumference of a semicircle}\\\\ C=\cfrac{\pi d}{2}~~ \begin{cases} d = diameter\\[-0.5em] \hrulefill\\ d=7 \end{cases}\qquad \implies \stackrel{\textit{circumference of all 3 semi-circles}}{3\left( \cfrac{\pi 7}{2} \right)\implies \cfrac{21\pi }{2}} \\\\\\ \stackrel{\textit{sum of all borders}}{\cfrac{21\pi }{2}~~+~~7}~~\approx ~~32.99+7~~\approx~~ 39.99[/tex]
