Question 786918
Albert leaves school driving to the East Bay at 20 mph. Two hours later, Johnny leaves school traveling at 30 mph. How long until they meet? 


Albert travels 40 km in 2 hours. when Johnny starts

distance when they meet =x
Time johnny takes to meet = t

t=d/r

Time taken by johnny+ 2hours = time taken by Albert 

x/30 +2 = x/20

x/20-x/30=2

(3x-2x)/60=2

3x-2x=2*60
x=120

120/30 = 4 hours from the time johnny starts