Answer
$0.018\ mm$
Work Step by Step
The mass in grams is: $12\ oz. \times \frac{28.4\ g}{1\ oz.} = 340\ g$
Given the density of $2.70\ g/cm^3$, the volume is: $V=340\div2.70=130\ cm^3$
The area in cm² is: $75\ ft^2\times\left(\frac{30.48\ cm}{1\ ft}\right)^2=70\times10^3\ cm^2$
Since the volume is given by: $V=A\times t$, the thickness is: $1.8\times10^{-3}\ cm=0.018\ mm$
