Remark
Part A
You would think what you wrote was correct, but it is not quite. The problem is the 200. That's an expense. You have the right number for the income from the students. The question, however, asks for the profit.
Profit = Income - Expenses
y = 15x - 200
Part B
Look at the graph below. You want the value of y when x = 10 for each of them. When you follow x = 20 on the line to the y axis, you find that y = 100. The solution point is (20,100). In other words, the profit is 100 dollars.
You could show that algebraically as well
x = 20 Given
y = 15*20 - 200 Substitute into equation
y = 300 - 200 Combine
y = 100 Answer
Graph
What the graph shows is that if they have 0 students, they still have to meet the rent and they owe 200 dollars (-200). The point on the graph is (0,-200)
Their break even point is a little over 13.3. That is if they have a total of 13.3 students, they make just enough to pay the rent. If they have 10 students each. They make 100 dollars. (20,100)
Conclusion
Equation: y = 15x - 200
Solution for 10 each: (20,100)
