Sarah and nancy each drive 600 miles. sarah's average speed is represented by x miles per hour. what does the denominator of the rational expression 600/x−4 mean in the context of this situation? a) the denominator represents nancy's average speed if she averages 4 mph less than sarah. b) the denominator represents the time required for nancy to drive 600 mi. c)the denominator represents nancy's average speed if she averages 4 mph more than sarah. d)the denominator represents the time required for sarah to drive 600 mi.