Answer:
1. 36 rocks in total.
2. 15 purple rocks more than blue rocks
Explanation:
1. Purple rocks are
of all rocks, then the remainder is
of all rocks.
2. Blue rocks are
of the remainder, then blue rocks are
of all rocks.
3. Silver rocks are the rest, that is
of all rocks.
4. It is known that the number of silver rocks is 3, then if x is the number of all rocks,
of x is 3:

Hannah has 36 rocks in total. 3 of them are silver,
are blue and
are purple. Then she has
more purple rocks than blue.