Find the slope of the line. That will give us the present price for each lunch.
Use the points (0,-150) and (50,0):
[tex]\begin{gathered} m=\frac{0--150}{50-0} \\ \Rightarrow m=3 \end{gathered}[/tex]
Then, the current profit equation is given by:
[tex]y=3x-150[/tex]
We want to change the price of each lunch so that the point (30,0) belongs to the graph (that means that when selling 30 lunches, it begins to make profit).
Let M be the new price. Then:
[tex]\begin{gathered} 0=30M-150 \\ \Rightarrow30M=150 \\ \Rightarrow M=\frac{150}{30} \\ \therefore M=5 \end{gathered}[/tex]
Therefore, the school should charge 5 dollars for each lunch.
