please answer this question

A 20 -year, 10%, 1,000 bond that pays interest half-yearly is redeemable (callable) in twelve years at a buy-back (call) price of 1,150. The bond's current yield-to-maturity is 9.50% annually. You are required to determine (i) the yield-to-call, (ii) the yield-to-call if the buy-back price is only 1,100, and (iii) the yield-to-call if instead of twelve years, the bond can be calied in eight years, buy-back price being 1,150