Assuming you are referring to simple interest not compound that that it is annual you would gain $100 putting you at $600
1/4n-8=1/4 would be first because it says less than so you switch it. then you put the 8 since it's in the same subtraction problem. Then the word "is" indicates the equal sign. and the n represents "a number" since it is unknown.
Answer: 320ft^3
Step-by-step explanation:
Assuming the pyramid is just a normal rectangular pyramid and isn't made of stairs...
10x8x12/3 = 320 ft^3