The Figure Given Below Shows the Cost Curves of a Firm

The figure given below shows the cost curves of a firm. Figure 8.3 ATC: Average Total Cost
AVC: Average Variable Cost
MC: Marginal Cost
Refer to Figure 8.3.If the firm maximizes profits at 120 units of the output, calculate the firm's marginal revenue.

A) $35
B) $40
C) $55
D) $4, 200
E) Cannot be determined from the information given.