My clock in the lounge room is 10 minutes slower than the clock on my phone which is 6 minutes slow. My tram always leaves 6 minutes early although it is scheduled for 8:55 it takes me 20 minutes to get to the tram stop what time must I leave according to my lounge room clock in order to catch my tram

So, the tram is scheduled to be about at 8:55, but it always leaves earlier by 6 minutes, so it really doesn't leave at 8:55 but 6 minutes before or 8:49, so you better be there at 8:49 to catch it.

the Phone Clock is slower by 6 minutes, so 8:49 on the phone will really be 8:43.

the Lounge Clock is slower than the Phone's by 10 minutes, so 8:43 on the phone is really 8:33 on the Lounge's Clock.

now to get to the tram stop, it takes you 20 minutes, so you can't go at 8:33 according to the lounge clock unless you're flash gordon, but you're not, it takes you 20 minutes to get there, so you need to leave 20 minutes before that, or 8:33 - 20 minutes, 8:13.