Not sure what you're referring to... our atmosphere is mostly nitrogen/oxygen - both gases were created by very massive stars, many times greater than our sun - our sun isn't massive enough to create the gases needed for our atmosphere...
I'm not from that school but I can help you.
Answer:
a) 
Now we can replace the velocity for t=1.75 s

For t = 3.0 s we have:

b) 
And we can find the positions for the two times required like this:
And now we can replace and we got:

Explanation:
The particle position is given by:

Part a
In order to find the velocity we need to take the first derivate for the position function like this:

Now we can replace the velocity for t=1.75 s

For t = 3.0 s we have:

Part b
For this case we can find the average velocity with the following formula:

And we can find the positions for the two times required like this:
And now we can replace and we got:

Answer:
(a) 40.6 degree
Explanation:
When refraction takes place from slab to water, the critical angle is 60 degree.
Use Snell's law
refractive index of water with respect to slab



μs = 1.536
Now for slab air interface, the critical angle is C.


1 / 1.536 = Sin C
C = 40.6 degree