Please help i dont understand

Question:
Mrs. Magdalino kept records on how much she spent on gasoline and the maintenance of her car.  She found that it cost $485 to drive 500 mi in a month.
a)  Find the cost per mile.  Write an equation that relates the cost c for gasoline and maintenance of a car to the number of miles m the car is driven.
b)  Use the equation to find the cost for driving 1200 miles.
c)  About how many miles are driven for a cost of $820?


a)
$485/500mi = $0.97/mi

c = cost
m = miles driven

cost per miles driven = cost / mile driven = c/m

b)
(1200 mi)*($0.97/mi) = $1164

c)
(x miles)*($0.97/mi) = $820

*divide both sides by $0.97/mi

x miles = $820/($0.97/mi)

x = 845.36 miles