Answer:
45°
Step-by-step explanation:
If we consider a full rotation to be 360°, we can simply divide 360 by 8 to find 1/8 of a full rotation.
360 ÷ 8 = 45
1/8 of a full rotation is 45°
I set this up as an inequality,

. If you take the cubed root of 800, you get the lower bound of the side length, which is 9.2. Then I just worked my way up until I hit the first number that put me over a volume of 800. That number is 9.29, because 9.28 cubed is 799.1 (not high enough) and 9.29 cubed is 801.8. Therefore, the bounds of the sides exist within a conjunction:

. That's the best I could come up with to help on that one. Wasn't sure if there was another method you were taught at school. I just used common sense more than any rule.
Step 1. identify the length of both bases
Step 2. Add the lengths of the bases
Step 3. Identify the height of the trapezoids
Step 4. Multiply the sum of the lengths of the bases by the height.
Step 5. Divide the results by two and then theres your answer.
More information is required to answer the question correctly.