Given the information on the picture, we have the following rectangular pyramid:
Notice that we get the following right triangle:
then we can use the pythagorean theorem to find the missing length:
![\begin{gathered} L^2=(29)^2+(12.5)^2 \\ \Rightarrow L^2=841+156.25=997.25 \\ \Rightarrow L=\sqrt[]{997.25}=31.58 \\ L=31.58in \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/udfwqys44kpxs83wa2065e09lqcym8xs7m.png)
Now we have the base and the height of a lateral side:
Then, using the formula for the area of a triangle, we get the following:

therefore, the lateral area of the rectangular pyramid is 394.75 in^2