Bless you. :)
Just to expand on my original post, if you want a more accurate graph you'll want to see the step change in semi-variable costs (i.e. 100 to 101, 300 to 301). You can display this by expanding the data range as follows:
Units Variable Costs Semi-Variable Costs Fixed Costs Total...
The key to solving this is understanding what information you need to display and then work backwards from there.
Units
Income
Total Cost
Units: You need to calculate the values at 100,200,300,400,500, so they becomes the 5 fixed rows in your spreadsheet.
Income: =Units*11.50
To simplify...