Answer:
about 1325 mph
Step-by-step explanation:
average speed = total distance / total time= (distance uphill + distance downhill) / (time uphill + time downhill)
time uphill = 606060 minutes / 60 = 10101 hours
path = 666 mph * 10101 hours = 6727266 m
time downhill = 6727266 m / 10101 hours = 55.5 h
average speed = (6727266 m + 6727266 m) / (10101 hours + 55.5 h) = about 1325 mph