Use a 5 percent discount rate to compute the NPV of each of the following series of cash receipts and payments.

a. $6,200 received now (year 0), $1,890 paid in year 3, and $4,000 paid in year 5.
b. $10,000 paid now (year 0), $12,690 paid in year 2, and $31,000 received in year 8.
c. $20,000 received now (year 0), $13,500 paid in year 5, and $7,500 paid in year 10.