Question 262982
It is not clear if they are heading towards each other or heading to the same place and who is further ahead.
If they are heading towards each other.
50t+40t=15
90t=15
t=1/6 hr =10 minutes if heading towards each other


If the slower car is 15 km ahead
then 40t+15=50t
15=50t-40t
15=10t
15/10=t
1.5 hrs forthe 50 kph to catch up

if the 50 kph is ahead by 15k
50t+15=40t
15=-10t
15/-10=t
-1.5 hr=t
time can't go backwards so the slower car can never catch up.