Difficulty with Troder question

Hello Sir, I am stuck with troder question from very first day I tried doing it and it was my 5th attempt today I have watched all ur lectures on interest rate collars and I am very comfortable with the theory behind. But still I can't solve trover, question no 54 of BPP kit on my own without referring back to solution. I think if same question comes in next exam i probably get the full marks on theory and would fail on computation. I have tried doing it so many times that I have root learned the whole solution but everytine i try to put my brain in I lost the track. Could you please consider putting up a ravion lecture on this question. Majority of students may've been struggling with this question. Thanks