Answer
(a) $10^{10}~gallons/year$
(b) $10^{9}~lb/year$
Work Step by Step
(a) We estimate that the number of plastic gallons purchased in the U.S. is 30 millions ($3\times10^{7}$) per day. A year has 365 days.
$(3\times10^{7}~gallons/day)(\frac{365~days}{1~year})\approx10^{10}~gallons/year$.
(b) The weight of each gallon container is about $0.1~lb=10^{-1}~lb$.
$Total~weight=(10^{10}~gallons/year)(\frac{10^{-1}~lb}{1~gallon})=10^{9}~lb/year$.
