How to find Effective annual rate of discount in part (a)?

2. The commercial rate of discount per annum is 18% (this means that simple discount is applied with a rate of 18%). (a) We borrow a certain amount. The loan is settled by a payment of 1000 after three months. Compute the amount borrowed and the effective annual rate of discount. (b) Now the loan is settled by a payment of 1000 after nine months. Answer the same