*long day my brain hurts* i just need to know one answer

student tickets cost 5$ each adult tickets cost 10$ each a total of 4,500$ was collected. 700 tickets were sold.

write a system of equations that can be used to find the number of student tickets, s, and the number of adult tickets, a, that were sold at the playoff game

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?