Stereo Sound Unlimited Has a Monopoly Over the Installation of Surround

Multiple Choice

Stereo Sound Unlimited has a monopoly over the installation of surround sound systems. If Stereo Sound Unlimitedʹs total revenue from installing 10 sound systems is $20,000 and its total revenue from installing 11 sound systems is $19,000, what is the marginal revenue of the eleventh sound system?

A) -$2,000
B) -$1,000
C) $2,000
D) $3,800