Et y represent the number of students in the group who are not members. You can write an expression for y in terms of x from the information given. What do you know? The total number of students = 19 x + y = 19 which gives you y = 19 - x OR you also know the total cost is 209 and you can use that and the cost of the two types of tickets to obtain an expression for y in terms of x.
