Graphing Multivariable Equations

[DDE12]

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?

[shg]

Wleocme to the board.

Solver is a built-in tool in Excel that will solve, among other things, linear programming problems like yours. See http://www.solver.com/excel-solver-optimization-methods

[DDE12]

Thanks for the tip shg. With a combination of web searching and trial & error, I came up with the following table and solver parameters.

Solver table.JPG

The formula for F14 is =SUM(F2:F13)-(3*(8-$D$14)) This will account for the $3 loss for empty display bushels.
The solver parameters are:
Target Cell: $F$14 Equal to: Max
By Changing Cells:
$D$2:$D$13
Constraints:
$D$14 <= 8
$D$2:$D$13 = integer
$D$2:$D$13 >= 0
$E$14 <= 100
With Options:
Max Time: 300 seconds
Iterations: 30000
Precision: 0.000001
Tolerance: 0.000001 %
Convergence: 0.001
Select Assume Linear Model (when left unselected I would still not get integers for the number of bushels despite that being a constraint.)
Tangent, Forward, Newton

[shg]

Good job, thanks for posting back.