Answer:

Step-by-step explanation:

You split it up into two 3-D triangles.

One of them has a volume of ((6*(5+5))/2)*8 = (60/2)*8=240

For the other one, you are missing a side on the 2-D face, so in order to apply pythagorean's theorem you need to split it into two more triangles. You know that 13^2=5^2+x^2    169-25=x^2         144=x^2  x=12

now that you know the missing side of the triangle you can recombine them. The volume of the remaining 3-D triangle is (((5+5)*12)/2)*8 = 60*8=480

480+240=720 meters cubed