Atriangle prism has a surface area of 350 square feet, a length of 15 feet, a height of 10 feet, and a of side of 5 feet. find the width of the triangular prism.

 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".