Can someone tell me which values to use when using the standard devation function (STDEV) in excel?

Also, could someone tell me which values to use when using the Slope function in excel (part C)

And check my work on the rates of return and average if you can too please!!

Thank you!!

Risk & Beta
Year	Facebook (FB) Stock Price	Twitter (TWTR) Stock Price	Market (S&P 500 market index) Value
2015	$105.02	$23.14	1,637.51
2014	$78.45	$36.56	1,543.52
2013	$53.32	$60.01	1,237.52
A) Rates of return
Year	FB	TWTR	Market
2015	9.28%	-12.91%	-12.91%
2014	13.63%	13.63%	-17.96%
2013	11.64%	11.64%	-108.90%
Average	11.52%	4.12%	-46.59%
B) Standard Deviation of Returns
FB	TWTR	Market
C) Graph Stock Returns and Market Returns
FB	TWTR
Slope from linear trendline	Slope from linear trendline