This is honestly not something I’ve learned. The answer is something I don’t know.
Let 
be the average acceleration over the first 2.46 seconds, and 
the average acceleration over the next 6.79 seconds.
At the start, the car has velocity 30.0 m/s, and at the end of the total 9.25 second interval it has velocity 15.2 m/s. Let 
be the velocity of the car after the first 2.46 seconds.
By definition of average acceleration, we have
and we're also told that
(or possibly the other way around; I'll consider that case later). We can solve for in the ratio equation and substitute it into the first average acceleration equation, and in turn we end up with an equation independent of the accelerations:
Now we can solve for . We find that
In the case that the ratio of accelerations is actually
we would instead have
in which case we would get a velocity of
The correct answer is b , the the liquid with heat and cool faster
When Alana moving 19km/h, a stationary object will be perceived by her as moving toward her with 19km/h velocity. If the object is not stationary(velocity isn't zero), the speed will increase by the object velocity.
the relative speed of the tennis ball=
the speed of Alana + true speed of the tennis ball
19km/h+ 11km/h= 30km/h
