For this case we have that by definition, the volume of a cuboid is given by:

Where:
L: It's the long
A: It is the width
h: It is the height
According to the problem data we have:

So, the volume of the cuboid is:

Finally, the volume of the cuboid is: 
Answer:

Subtract 5 from both sides
a/-8 = 4/7 - 5
simplify 4/7 - 5 to 31/-7
a/-8 = 31/-7
multiply both sides by 8
-a = 31/-7 x 8
simplify 31/7 x 8 to 248/7
-a = 248/7
multiply both sides by -1.
The answer is a = 248/7
The words are the explanations of the steps and the dark bolded words are the work shown for each step.
Arranged in descending order means the terms are arranged in the order of the exponent, from the largest to the smallest. the exponent is the little number up right to y,
3y^4+6y^3+2Y^2-5y
so the third term is 2y^2