The question is determine the thickness in cm of a rectangular piece of aluminum foil that is 17.0 inches long and 3.0 inches wide,with a mass of 2.21 grams. The density of aluminum is 2.70 g/cm.
I do not know how to set this up or how to get the answer.  Thanks everyone for helping me.
			
			
			
				use 
density = mass/volume 
volume = mass/ density 
now volume = L x B x H 
H--thickness 
L- length 
B- width 
calculate volume and then finally thickness.