I am working on a project for school and there is one question I do not understand. Could someone please help me?

Project:

1.Find the high temperature for a certain city in the US. Use the internet to find temperature on July 1 of each year from 1987 to 2007. Make a table with the year in the first column and the corresponding temperature in the second column.

Ok, I gathered all of my data for and made a table.

2.Let x = 7 for 1987, x=8 for 1988, etc… Using Excel input the x values into column A and the high temperatures in column B. Highlight the cells A1 to B21. Click the insert tab at the top of the screen. Then click on the “Scatter” icon in the middle of the tool bar. Select the first icon in the first row for your graph type. This will make a scatter plot of your data. Select a chart type from the tool bar that allows a title, an x-axis label, and a y-axis label. Label each of these for your specific project. Save and print the scatter plot.

I created my scatter plot:

http://i333.photobucket.com/albums/m...g?t=1217452117

Ok, here is the part I do not understand what to do:

3. Calculate by hand the line passing through your ordered pairs for the year 1987 and 2007. You must show your work. Now use this line to predict the values at 5 other years from 1987 – 2007. Record the difference from your model with the actual temperature for those years.

Am I supposed to use the point slope formula y = mx + b for finding 1987 and 2007?