How many different positive integers having six digits are there, where exactly on of the digits is a 3, exactly two of

How many different positive integers having six digits are there, where exactly on of the digits is a 3, exactly two of the digits are a 4, exactly one of the digits is a 5, and each of the other digits is a 7 or an 8?

A) 360
B) 720
C) 840
D) 1,080
E) 1,440

[spoiler]OA=B[/spoiler]

Source: Princeton Review