Not quiet sure how to approach the following question;

you borrowed $4000 at an interest rate of 7% compounded semiannually. The loan is to be repaid by three payments. The first payment, $1000, is due two years after the date of the loan. The second and third payments are due three and five years, respectively, after the initial loan. Calculate the amounts of the second and third payments if the second payment is to be twice the size of the third payment.