How long would it take to travel to Pluto?
The spacecraft New Horizons launched in Jan 2006 flew by Pluto in 2015. It takes about six months to reach Mars. For Pluto, it is nearly 10 years
Mars mean distance from Sun is 1.52 AU. For Pluto, the least distance from Sun exceeds 30 AU. Roughly, the ratio of these distances is 20. Also, the actuals for spacecraft travels are nearly in the same ratio. A surmise: the average speed of getting away from Sun is nearly 3 AU per year.