Answer:

Step-by-step explanation:
The complete question in the attached figure
we know that
The volume of a cube is equal to

where b is the length side of a cube
In this problem we have

substitute in the formula

-----> by power of a product
----> by power of a power
Simplify

Answer:
20
Step-by-step explanation:
28/7=4
5x4=20
That's such a broad question, and super subjective. I'd probably say that you learn math effectively from a good teacher or tutor, or if you're an individual learner, perhaps a textbook or any kind of online resource.