Question 1171220
d=v*t
270=vt
and
270=(v+6)*(t-0.5)
therefore, vt=vt-0.5v+6t-3
and 0.5v=6t-3 so v=12t-6

therefore, 12t^2-6t-270=0 substituting
2t^2-t-45=0
(2t+9)(t-5)=0
t=5 hours
so normally the speed is 54 km/h 
at 60 km/h, 6 km/h faster, the trip will take 4 1/2 hours.

54 km/h