The volume of the prism is (B) 864 mm3
Let start off with 5/8+7/8= 1 4/8
Now it's 13+1 4/8= 14 4/8 or 14 1/2 :)
1) 8x-13
2)19r-19s
3)8m-10n
Solve in the parentheses then label the ones with the same variable and solve those setting up the equation with variable first. Do check this I am not perfect.
Hope this helped! ;)