Could you please explain step by step how to resolve this question? Thank you :)

Stryker Industries received an offer from an exporter for 15,000 units of a product at $17.50 per unit. The acceptance of the offer will not affect normal production or domestic sales prices. The following data are available:

Domestic unit sales price	$20
Unit manufacturing costs:
Variable	11
Fixed	1

The differential revenue from the acceptance of the offer is

a.$262,500

b.$300,000

c.$250,000

d.$52,500