First, to find the slant height, we use Pythagorean's Theorem to find the slant height, as the image below shows.
Then,
![\begin{gathered} h^2=10^2+7.5^2 \\ h^2=100+56.25 \\ h=\sqrt[]{156.25} \\ h=12.5ft \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/h699u3nmswnu96izk3p8y5axstaa7emsx0.png)
The slant height is 12.5 feet.
Now, the surface area formula is

Where s = 12.5 and b = 15.

Hence, the surface area of the pyramid is 600 square feet.