For the first question, there are just four groups. Those that just watch TV, those that just read, those that do both and those that do neither. You've worked out numbers for the first two and you are given the number for the third group. If all four total 100 you should be able to deduce the fourth. (It's easy to see what's going on if you draw a Venn diagram).

For the second question, get what's going on straight in your mind by working through a long division using actual numbers. Try for example 1236/12, 12's into 1 don't go, 12's into 12 go once etc.