I know that Little's Law states (paraphrased):

the average number of things in a system is the product of the average rate at which things leave the system and the average time each one spends in the system, or:

n=x*(r+z);
x-throughput
r-response time
z-think time
r+z - average response time

now i have question about a problem from programming pearls:

Suppose that system makes 100 disk accesses to process a transaction (although some systems require fewer, some systems will require several hundred disk access per transaction). How many transactions per hour per disk can the system handle?

please help