A car is traveling at a constant velocity. After two hours the car has traveled 110 miles. After four hours the car has traveled 220 miles. Assuming a linear equation fits this situation, find the linear equation for the given data?

The velocity is
  (220 mi - 110 mi)/(4 hr - 2 hr) = (110 mi)/(2 hr) = 55 mi/hr
We recognize that the car started at 0 miles, because the first data point is 2 hours and 110 miles (110 mi = 2 hr*(55 mi/hr)).
  miles traveled = (time in hours)*(55 miles/hour)