Both these problems can be worked in the same way. It is helpful to start by making a table listing all the possibilities. Then, fill in the numbers the problem statement tells you (black) and solve for the remaining numbers (blue) by making the totals come out right.
11. The appropriate choice is D) 115.
12. Here, you're given percentages, so you need to convert them to numbers of students. You do that by multiplying each by the total number of students. If you do the problem using a spreadsheet, you can let it do the math for you. The numbers of students are shown in the attachment.
The appropriate choice is A) 120.