Please help with this question about Operating System:

The following System has CPU (average time to execute 1,000 instructions): 1.2ms and Four Hard Drives with the following average Seek Times:

Drive A: 35ms Drive B: 10ms Drive C: 5ms Drive D: 50ms and Track Requests (unordered): 31, 20, 15, 20, 31, 15 (Assume drive heads start at track 0)

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

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

3 - 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)?

4 - 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