A town N is 340 km due west of town G and town K is west of town N. A helicopter Zebra left G for K at 9.00 a.m. Another helicopter Buffalo left N for K at 11.00 a.m. Helicopter Buffalo traveled at an average speed of 20 km/h faster than Zebra. If both helicopters reached K at 12.30 pm find the speed of helicopter Buffalo.