When Sam's Scarves Uses 2 Knitting Machines and Employs 3

When Sam's Scarves uses 2 knitting machines and employs 3 people, total revenue is $330 a day. When Sam's Scarves uses 2 knitting machines and employs 4 people, total revenue is $360 a day. The value of marginal product of the third worker is

A) $110.
B) $30.
C) $360.
D) $90.