AHSME 1995 Problem 5

A rectangular field is 300 feet wide and 400 feet long. Random sampling indicates that there are, on the average, three ants per square inch through out the field. [12 inches = 1 foot.] Of the following, the number that most closely approximates the number of ants in the field is

$\mathrm{(A) \ \text{500 thousand} } \mathrm{(B) \ \text{5 million} } \mathrm{(C) \ \text{50 million} } \mathrm{(D) \ \text{500 million} } \mathrm{(E) \ \text{5 billion} }$