1pt this test: 20 pts if the mean of a the mean of the combined set is round to the nearest santh as needed)

Can someone me with this problem i don't understand i need

Another type of subtraction equation is 16-b=7. explain how you would sole this equation then solve it.

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?