For this case we have the following profit function:
And we are interested on find the profit after selling 700 pretzels, so we just need to replace X=700 into the profit function like this:
The profit function is on the figure attached. We see that for 0<X<217 we have negative profits, and for X>217 we will have positive values for the profit. And also we can see that for X=700 we have a profit of approximately 169.