Sinking Fund

Please help. I can’t figure out this anwser. Its in Book 5 of the Schweser: The 10.80% bones of PPL Corp mature on Jan 15, 2019 and currently at 104. It is semi-annual and has a Jan. 25 coupon date. If today is Jan 15 it has a maturity date of 11 years. The bond has a Sinking Fund requirment drawn randomly accordingliny: Years 1-6 (no requirment) year 7 (20%) year 8 (20%) year 9 (20%) year 10 (20%) year 11 (20%). A. - What is the expected yeild to maturity B. - What is the duration and convexity.

Posted on LI forum. Let’s try not to post the same question in multiple forums because we just get odd disconnects on threads.