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.