Kelsey correctly used the fermi process and the following estimates to determine how many books would fill a railroad car.

a book is about 1 ft long, 12 ft wide, and 15 ft thick.
a railroad car is about 60 ft long, 10 ft wide, and 10 ft high.

which equation could she have written?
6×1031×10−1=6×104
6×1031×10−1=6×102
6×1041×10−1=6×105
6×1041×10−1=6×103