Help please I don't understand this I've read over it a couple times and still don't get it

Ms.ortiz sells tomatoes wholesale. the function p(x)=-80x^2+320x-10, graphed below, indicates how much profit she makes on a load of tomatoes if she makes on a load of tomatoes if she sells them for 4-x dollars per kilogram. what should ms.ortiz charge per kilogram of tomatoes to make on a load of tomatoes?