T-shirt profits A clothing company makes a profit of $\$ 10$ on its long-sleeved T-shirts and $\$ 5$ on its short-sleeved T-shirts. Assuming there is a $\$ 200$ setup cost, the profit on T-shirt sales is $z=10 x+5 y-200,$ where $x$ is the number of long-sleeved T-shirts sold and $y$ is the number of short-sleeved T-shirts sold. Assume $x$ and $y$ are nonnegative.
a. Graph the plane that gives the profit using the window $$[0,40] \times[0,40] \times[-400,400]$$
b. If $x=20$ and $y=10,$ is the profit positive or negative?
c. Describe the values of $x$ and $y$ for which the company breaks even (for which the profit is zero). Mark this set on your graph.