Question 756061
This requires the use of the following formula:

distance(d) = rate(r) * time(t) and r = d / t

Paul's rate  = 3.75 / 15 = .25 km/minute
Lisa's rate  = 4.2 /  18 = .23 km/minute
Carol's rate = 3.2 /  12 = .27 km/minute
Eric's rate  = 5.5 /  30 = .18 km/minute

Carol's is the fastest rate