It is essential that you use the symbol " ^ " to denote exponention. See the following changes I have made.
9u^2v and which term or terms are like terms? 15u^2v. Why? because both have "u^2" in them.
In order to determine the correct answer, it would be helpful to set up equations. We do as follows:
Let x = students
y = adults
x + y = 215
.50x + 2y = 250
SOlving simultaneously, we have:
x = 120 students
y = 95 adults
Hope this answers the question. Have a nice day.