Question 38367
Remember D = RT, distance = rate*time.
Let Kim's rate be r.
Then Lucy's rate is r + 4.
They both travel for 2 hours, so t = 2.
Their total distance is 80 km, so we have
2r + 2(r + 4) = 80
2r + 2r + 8 = 80
4r + 8 = 80
4r = 72
r = 18 km/h, Kim's rate.