A lender studies the fact that at some point he can place at 3 possible debtors, in the simple interest regime, certain amounts as follows:
- to the first the amount of £1000 for 2 months with the percentage of 5%.
- to the second amount of £2000 for 100 days with the percentage of 6%.
- to the third the amount of £5000 for 10 weeks with the percentage of 8%.

In the meantime, another possible debtor appears. The lender wants to know:

a) what amount should he lend to the 4th debtor for a period of 3 months with the annual percentage of 4% to have the same interest as from the first 3 debtors together.

b) with what percentage should he lend the sum of £5,000 for one quarter to the 4th debtor to have the same interest as from the first 3 debtors together.

c) for how many days should he lend the amount of £4000 to the 4th debtor with a percentage of 10% to have the same interest as from the first 3 debtors together.