A lawnmower is rented at $200 per day plus a charge per hour of use. The lawnmower was used for 4 hours one day, and the total charge was $300. Which equation can be used to find the charge x, in dollars, per hour of use?
a 200+4x=300
b 200x+4=300
c 200x+4x=300
d 200+4=300x