Marius wrote:

> I can't think of a nice way to include the profit in this graph without adding another axis. Maybe someone else has a good idea.

One way is to include the level curves of profit as faint lines of the form

\[ 750 x + 1000 y = p \]

for various values of the number \\(p\\). The line for maximum profit will go through the upper right corner of the shape you drew in green.