I have this Operating System question that I need help[ with:

A system has the following characteristics:

CPU (average time to execute 1,000 instructions): 1.2ms

Four (4) Hard Drives with the following average Seek Times:

Drive A: 35ms

Drive B: 10ms

Drive C: 5ms

Drive D: 50ms

Track Requests (unordered): 31, 20, 15, 20, 31, 15

Note: Assume drive heads start at track 0.

Answer the following questions about the above system:

- Which drive would require the least amount of time to access all of the unordered track requests?

- Which drive would require the most amount of time to access all of the unordered track requests?

- If the track requests were reordered, which drive would require the least amount of time to access all of the track requests (assume reordering requires 1,000 instructions)?

- If the track requests were reordered, which drive would require the most amount of time to access all of the track requests (assume reordering requires 1,000 instructions)?

Thanks