I need help in excel with step-by-step instructions for calculations and tables.

Select 2 industry portfolios of your choice and download 36 months of data and download a market index (S&P 500 or Wilshire 5000) from finance.yahoo.com or a similar site.

I have chosen 2 industries and downloaded 36 months of WILSHIRE-5000. The industry portfolio data is in a monthly weighted average. How do I make the S&P 500 Index information a monthly weighted average?

S&P 500
Date	Open	High	Low	Close*	Adj Close**	Volume
1-May-18	2,642.96	2,742.24	2,594.62	2,705.27	2,705.27	76,011,820,000
1-Jun-18	2,718.70	2,791.47	2,691.99	2,718.37	2,718.37	77,891,360,000
1-Jul-18	2,704.95	2,848.03	2,698.95	2,816.29	2,816.29	64,898,300,000
1-Aug-18	2,821.17	2,916.50	2,796.34	2,901.52	2,901.52	69,523,070,000
1-Sep-18	2,896.96	2,940.91	2,864.12	2,913.98	2,913.98	63,031,510,000
1-Oct-18	2,926.29	2,939.86	2,603.54	2,711.74	2,711.74	91,930,980,000