Answer:
64 km/hr
Step-by-step explanation:
216 - 56 = 160 km on good road
216km / 48 km/hr = 4.5 hours total time
56 km / 28 km/hr = 2 hours on bad road
then 2.5 hours on good road ( for total 4.5 hrs)
160 km / 2.5 hr = 64 km/hr on the good road portion