Kenisha uses the Fermi process to estimate the number of dollar bills that would cover her driveway. Her driveway is rectangular in shape. She estimates a dollar bill to be about 6 in. long and 3 in. wide. She estimates her driveway to be about 30 ft long and 20 ft wide. Which expression should Kenisha use in the process?
a) 6×10²​/2×10¹
b) 6×10²​/2×10²
c) 9×10⁴/2×10¹​
d) 9×10⁴​/2×10²