For number of students equals to zero (s=0), you have the cost amount as following:
C = 0*4.5 + 50 = 0 + 50 = 50 dollars. So the first point on a graph will be (0, 50) (first number being the s coordinate-number of students, and the second number being the c coordinate-cost)
Because 0 students are going to the trip and no one will be paying 4.5 dollars, but 50 dollars
will be paid as the nonrefundable deposit (no matter if the students are going or not).
For s=1, cost will be: c = 1*4.5 + 50 = 4.5 + 50 = 54.5 dollars.
Because 1 students is going, he will be paying 4.5 dollars, and deposit of 50 dollars is always paid. So the point on a graph will be (1, 54.5).
For s=2, two students are going on the trip, cost will be:
c = 2*4.5 + 50 = 9 + 50 = 59 dollars.
The graph point will be (2, 59).
For three students s = 3, cost is:
c = 3*4.5 + 50 = 13.5 + 50 = 63.5 dollars.
Because each of the 3 students are paying 4.5 dollars and a one-time deposit is paid for the group which is going to the trip (50 dollars), so the total amount is 63.5 dollars. Point on a graph will be (3, 63.5). First coordinate of a point is 3 students (s=3) and the second coordinate is 63.5 (total cost in dollars).
For s=4 (4 students), cost is: c=4*4.5 + 50 = 18 + 50 = 68 dollars. Point with coordinates on a graph is (4, 68).
Etc. So for number of students going to the trip s=24, cost would be, as per formula c = s*4.5 + 50, c=24*4.5 + 50 = 158 dollars.
I attached a graph (.png image) for this math problem.