Answer
(a) There are 640 acres in a square mile.
(b) There 43,560 sq ft in an acre.
(c) There are $3.26 \times 10^5$ gallons in an acre.
Work Step by Step
It is known that 1 mile = 5280 feet and that 1 cubic foot = 7.477 gallons.
(a) The area of one acre is $\frac{1}{8}$ miles $\times \frac{1}{80}$miles = $\frac{1}{640}$ square miles.
(b) If 1 acre is 640 square miles, and 1 mile is 5280 feet, then clearly, 1 acre is $\frac{(5280)^2}{640} = 43,560$ sq ft.
(c) 1 acre-foot = $(43560 ft^3)\times(\frac{7.477 gal}{1ft^3}) = 3.26 \times 10^5 gal $
