Rewrite the expression in the form b^n b^-3/b4

This is so hard and it’s for a test

Aclassroom is made up of 11 boys and 14 girls. the teacher has four main classroom responsibilities that she wants to hand out to four different students (one for each of the four students). if the teacher chooses 4 of the students at random, then what is the probability that the four students chosen to complete the responsibilities will be all boys?

Pls the last one and it has to be like number 6