Walter Corp., a manufacturing concern, also has a subsidiary which specializes in the rental of the heavy equipment. Some customers prepay their rentals and other customers are billed periodically for rent owed.

The following are account balances of the year $2020$: $($see attached photo$)$

A$)$ What is the rental revenue for the year?

The following are account balances of the year $2021$: $($see attached photo$)$

B$)$ What is the cash inflow from rentals for the year?

Please answer this and explain how to find the answer, I$\text{'}$d like to learn. I will upvote!