In 4a the frequency for the last one is meant to be 4.
4b.
There are 6 out of 20 families that have one child, that is 6/20 I found an equivalent fraction so the denominator is 100: 30/100 If you multiply that by 100 to get a percentage you get 30%
5. I have included a picture of a pi chart I made on a word processing application.
Hope this helps :)