One vertical face is 150 ft^2.
Another vertical faces is 50 ft^2.
That leaves 10W for a third vertical face,
in addition to which, one has the two triangular bases.
If the bases were right triangles,
their width would be sqrt(15^2-10^2) = sqrt(125)
= 5 sqrt(5) = about 11.7 ft,
but this doesn't "work" because the area of the two bases
would be 58.5 ft^2 and 117 ft^2 for the 3rd vertical face,
for a total surface area of about 375 ft^2.
Hence, the angle between the "side" and the "width" is larger than 90 degrees.
However, I'm assigning the name "theta" to the angle between "side" and "length".