全部いわゆる tough 構文 ⇔ 形式主語構文の書き換えです。
1. a: This book is very hard to understand.
b: It (is) very (hard) to (understand) this book.
2. a:The problem of AIDS is difficult to solve.
b: It is (difficult) (to) (solve) the problem of AIDS.
3. a: It wasn't easy for me to remember her name.
b: Her name wasn't (easy) for (me) (to) (remember).