Hi,
Let r and t represent the speed and time for the truck
Write as we Read*** D = r*t for the truck and car
r*t = 360km r = 360km/t
(r+20kmph)(t-3hr) = 360km substituting for r so as to solve for t
(360/t + 20)(t-3) = 360km
360t + 20t^2 -3*360 -60t = 360t
20t^2 -60t - 3*360 = 0
t^2 -3t - 54 = 0
factoring
(t-9)(t+6) = 0 tossing out negative solution
t = 9hr r = 40kmph for the truck
CHECKING our Answer for car:
60kmph*6hr = 360km