Graphing Multivariable Equations

How would I use Excel to create a graph that would help me to solve problems like the following hypothetical situation?
I am a fruit stand owner and have $100 to spend to purchase up to 8 bushels of fruit from the market to sell in my fruit stand. I will then set various prices to sell the fruit.
The market has 12 different kinds of fruit, all with different prices.
I can purchase up to 8 bushels of fruit (I could purchase bushels of all of the same fruit or combination of the 12 various fruits). I want to spend all or nearly all of the $100 but don't have to purchase 8 bushels. I could purchase only 5 bushels if that would maximize my profit. I have space to display 8 bushels and for every space left empty I lose $3.
What I need to know is- how many bushels of which fruits do I need to purchase to maximize profit?

I think I can use Excel to create a graph with the different combinations of purchasing the fruits for the $100 I have to spend and display the profits from those purchase combinations. How do I do this?