20.it isnt hot enough for us to go out
22.it is too ripe for us to eat them
21.it isnt difficult enough for you to do them
 

20 It's warm tonight. We can go out.
-> It's warm enough tonight for us to go out
21  These exercises are easy. You can do them.
-> These exercises are so easy that you can do them
22 Those oranges are ripe. We can eat them.
-> Those oranges are so ripe that we can eat them
23 My sister wasn't well. She didn't go to work.
-> My sister wasn't well enough to go to work
24 The book is small. I can put it in my pocket.
-> The book is so small that I can put it in my pocket