Let the distance between Logan airport and Framingham be x, then the speed of the car is x/20 and the speed of the bus is x/30.
Let the distance travelled by the car at the point they met be a, then the distance travelled by the bus is x - a.
At the time they met, a/(x/20) = (x - a)/(x/30)
20a/x = 30(x - a)/x
20a = 30x - 30a
50a = 30x
a = 3/5x
Therefore, they met after a/(x/20) = (3/5x)/(x/20) = 12 mins.
