If I walk at 5 km/hour; I miss a train by 7 minutes. If however, I walk at 6 km/hour I reach the station 5 minutes before the departure of the train. Then the distance between my house and the station is

Answer 1

the difference in time is 12 minutes
since time = distance/speed,

d/5 = d/6 + (12/60)
d = 6

check:

6km at 6km/hr = 1 hour
6km at 5km/hr = 1.2 hours = 1 hr 12 min

Answer 2

should it be this
d/5 = d/6 + (12/60)
or
d/5 - d/6 = (12/60)

Answer 3

Umm, looks the same to me.

a = b+c
is the same as
a-b = c