Disaggregating Return on Assets over Multiple Periods Following are selected financial statement data from 3M Company for 2012 through 2015.

$ millions Total Assets Net Income Sales 2012 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $33,876 $4,444 $29,904 2013 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33,550 4,659 30,871 2014 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31,209 4,956 31,281 2015 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32,718 4,833 30,274 Required

a. Compute 3M Company’s return on assets for 2013 through 2015. Disaggregate the ROA into the profit margin and asset turnover for 2013 through 2015. What trends do we observe?

b. Which ROA component appears to be driving the trend observed in part a? Explain.