7. Suppose that a RISC machine uses 5 register windows. a. How deep can the procedure calls go before registers must be saved in memory? (That is, what is the maximum number of "active'' procedure calls that can be made before we need to save any registers in memory?) b. Suppose two more calls are made after the maximum value from part (a) is reached. How many register windows must be saved to memory as a result? c. Now suppose that the most recently called procedure returns. Explain what occurs. d. Now suppose one more procedure is called. How many register windows need to be stored in memory?