The foil is only
You have to convert to a consistent set of units. We shall use grams for the mass unit and centimeters for the length unit.
The area of the foil is then
The mass isj
And then the thickness is the volume divided by the area:
The critical calculation here is the volume, after all of the conversions. The conversions are more tedious and a potential source of errors than anything relevant to the real question. We want a final answer in metric units (mm), so it may be best to first put all of the data into metric units at the millimeter level.
NOW we have:
The desired thickness calculation is: