The directions read as follows, but I'm unsure how to get a start on this.

See data worksheet for this problem, where you'll find 5 years of weekly returns for the S&P 500. You will want to copy that data here in order to create your spreadsheet.

a. Set up a spreadsheet to calculate the 26-week moving average of the index.

Note: In order to create the 26-week moving average for the S&P 500, convert the weekly returns to weekly index values using a base of 100 for the week prior to the first week of the data set. Set the value of the index at the beginning of the sample period equal to 100 + the S&P 500 Return value for that week. The index value in each week thereafter is then updated by adding the previous week's Index level to the current week's S&P 500 Return value. Then, graph the resulting S&P 500 values and the 26-week moving average, beginning with the 26th week of the data set. Use Excel's Chart Wizard and save the chart to a new page.

How do I calculate the first part of this chart in Excel?

Week of	S&P 500 return	S&P 500 Index Value	Moving Average
2-Jun-2014	7.20	100.00
9-Jun-2014	-1.37
16-Jun-2014	0.52