Hi Crystal! If I understand correctly, your question is more about how to graph the equation, rather than solving it, since the values for t are already determined (e.g., the years 1985 through 2000). For example, if t = 1988, then P = 1988 times 5.9 minus 11706, which comes to 23.2.
To find all the values for P, you can calculate them manually (like above), but I'd recommend using a spreadsheet. Start in cell A1 and enter 1985 (for the first year). Put the rest of the years down column A until you have the value 2000 in cell A16. Next, put your formula in cell B1. The formula should look like this: =A1*5.9-11706 (where A1 refers to the cell address in the spreadsheet, and * is the multiplication symbol). Copy the formula down column B, from cell B1 to cell B16. You can now find the answers to parts a and c of your question.
To plot the graph, highlight the range B1 through B16, and select Insert > Line > Line chart to create a simple graph of your equation. Hope that helps!