(perms/combs) how do you get the second part of this question?

[meager fulcrum]

If you see the science books as a single element, there are 4 possible places to place them between the geography books.
_g_g_g_

[meager fulcrum]

You can also see it initially as if it were 4 elements, 3 geography books and 1 block of science
In how many ways can you place 4 different elements in a row?

yeah, but we must also consider the ways in which science books can be inside the block

Since there are also four, it is also 4!

you consider them independently,
You only have the 4 different science books so how many ways can you arrange them, 4! too

Now we just multiply the probabilities that we obtained separately

Imagine that you flip a coin twice, what is the probability of getting Heads twice?

Yes, you multiplied each case (1/2)*(1/2) to obtain the joint probability

ok, let's do it with a simpler case,
You have 2 science books, which must be together, and one of geography.
the possible mixtures between geography books is 1 because it is alone
The possible mixes between science books are 2
C1-C2 or C2-C1
2!
and there are two possible places where the science books could go
_g_
To the left or right of geography book

then the total possibilities are: 1* 2 * 2 = 4