Call his normal time to reach school = T
And 8 min = 8/60 hr = (2/15) hr
And rate x time = distance....so....equating distances we have
(9/2)(T + 2/15) = (9/2 +1) ( T - 2/15)
(9/2 ) ( T + 2/15) = (11/2) (T - 2/15)
(9/2)T + (9/15) = (11/2)T - 11/15
(11/15) + (9/15) = (11/2) T - (9/2)T
20/15 = T = (4/3) hr
So...the distance is
(9/2) ( 4/3 + 2/15) =
(9/2) ( 22/15) = 33/5 km = 6.6 km