Hydraulic engineers in the United States often use, as a units of volume of water, the acre-foot, defined as the volume of water that will cover 1 acre (where 1 acre = 43560 ft2) of land to a depth of 1 ft. A severe thunderstorm dumped 2.8 in. of rain in 30 min on a town of area 42 km2. What volume of water, in acre-feet, fell on the town?