math!

Every minute.....the correct tme  is  (6/5) of a minute ahead of our clock

To see this......50 minutes after noon by  our clock  = 12:50PM.....but.....the correct tme is (50) * (6/5)  = 10 * 6  = 60 minutes after noon  =1 PM

And 100 minutes after noon  by our clock = 1:40PM but the correct time is 100 * (6/5)  = 120 min after noon  = 2PM

So  when our clock shows 3PM   (180 minutes after noon)....the correct time is actually 180 (6/5)  =

36 * 6   =   216 minutes after noon  =    3 hrs 36 min after noon  =  3:36 PM 

Since the correct clock is: 60 / 50 =1.2 or 20% faster for every minute of the slower clock, it therfore follows that in 3 hours or 180 minutes on the slower clock will be: 180 x 1.20  =216 minutes or 3 hours and 36 minutes on the regular clock.