How long would it take you to travel to the Andromeda galaxy at an average speed of 20mph?

The Andromeda galaxy is around 2.5 million light years away, but is moving towards out galaxy at a speed of about 100 to 140 kilometres per second (62 to 87 miles/sec). Our galaxy will collide with it in around 4.5 billion years. A long time, but you wont get far travelling at 20mph in that time, on an astronomical scale anyway, barely outside our own solar system.