If one of the variables is changed, that tells nothing about what happens to the other one, or IF anything happens, or when, or how long it lasts. Because they are UN-RELATED. You just said so yourself.
None of the choices says this.
Answer:
towards west
Explanation:
As we know that the speed of the blue car as appear to the bicycle rider is given as
towards west
also it is given that bicycle is moving at speed of 10 km/h towards East
so here we have

so we have

towards west
now speed of the red car is given as 15 km/h towards west
so here the relative speed of blue car with respect to red car is given as

towards west
Answer:
Time required by boat 1 for the round trip is less than that of boat 2.
Hence, boat 1 wins.
Explanation:
Case 1: Boat 1
Speed of boat = 
time = 
While going to another end
time = 
time = 
time = 1 hour
While going back,
time = 
time = 
time = 1 hour
Total time taken by boat 1 is,
Total time by boat 1 = 1 hour + 1 hour = 2 hour
Total time by boat 1 = 2 hour
Total time taken by boat 1 for the round trip is 2 hour.
Case 2: Boat 2
Speed of boat = 
time = 
While going to another end
time = 
time = 
time = 2 hour
While going back,
time = 
time = 
time = 0.66 hour
Total time taken by boat 2 is,
Total time by boat 1 = 2 hour + 0.66 hour
Total time by boat 1 = 2.66 hour
Total time taken by boat 2 for the round trip is 2.66 hour.
Time required by boat 1 for the round trip is less than that of boat 2.
Hence, boat 1 wins.