How to write it (all) from Peking University Teacher's edition, I've written it myself, I didn't look at it carefully at first. I thought it was very difficult

How to write it (all) from Peking University Teacher's edition, I've written it myself, I didn't look at it carefully at first. I thought it was very difficult

121-66 = 55 (set) 66 / 121 = 0.545 = 54.5%