let p be the number of peach trees she can buy
since the cost of a blueberry bush is $2.50, the money spent on bluberry bushes would be 2.5b
since the cost of a peach tree is $5.50, the money spent on peach trees will be 5.5p
we do not want the money spent to exceed $500, so we want the inequality:
2.5b + 5.5p <or= 500
to plot this, we just choose what tree we want on which axis.
let's say you want to plot blueberry bushes on the x-axis, and peach trees on the y-axis, then your graph would be graph1. the area under the line and above the positive side of the x-axis should be shaded. any point in this region represents a combination of each tree that can be bought. the points on the line are included, but that's only if she wants to spend the whole $500.
if you wanted to plot the peach trees on the x and the blueberries on the y, you would obtain graph2. again, you want to shade the area under the graph and above the positive side of the x-axis.