I'm sorry. I was expecting to receive an email notification but did not get one, and I am not on this website 24/7. I did not intend to come off as unappreciative.
As for the correct answers, the answer to part A is 20. A pair of white chairs must be separated by one red chair. The red chairs can be arranged like _ R _ R _ R _ R _ R _ with 6 spaces to put the white chairs. Then 6 choose 3 = 20. Part B is not so clear to me, so I'm not sure of the correct answer.