speed = distance/time
distance = speed * time
Carlos traveled for 2 hours.
Julia traveled for 1 more hour, or 3 hours
Carlos:
time = 2
distance = d
speed = 30 mph
distance = speed * time
d = 30 * 2
d = 60 miles
They both traveled 60 miles.
Julia:
time = 3
distance = 60 miles
speed = s
speed = distance/time = (60 miles)/(3 hours) = 20 mph
Julia's speed is 20 mph.