The average diameter is (this is the difficulty) 3.2+4.0/2=3.6cm.

Plastic wrap 60 meters = 6000 cm long.

Then a * * * has 6000/(3. 14*3.6)=530 floors.

Then the thickness is 0.5 * (4.0-3.2)/530 = 7.54/10000 = 0.000754 cm.