Mr. Snyder begins traveling east on Interstate 90 from Spokane with a full tank of gasoline. His car has a 15-gallon gas tank and gets 30 miles per gallon during highway travel. Let m = the number of miles Mr. Snyder has driven Let g = the number of gallons of gas remaining in his tank Select in the letter of the equation that describes the relationship between the number of miles Mr. Snyder has traveled and the number of gallons remaining in his gas tank.