a. To make the graph, plot the points for x and y, where x is the number of layers since it is the independent variable and y is the number of pennies since it is the dependent variable. After plotting, it should be relatively easy to tell the rate of change, or the slope, which is about 10 pennies per layer.
b. I would predict 35 pennies since 3.5 layers is between 3 and 4. Since for 3 layers, it takes 29 pennies to break and for 4 layers it takes 42, 35 is a reasonable in between.
c. I would predict 80 pennies. Refer back to in part a where the rate of change is about 10 pennies per layer. This can be represented as y=10x. If you plug 8 in for y, the outcome is 8*10=80