96 necklaces
To find out how many necklaces Camilla can make, we need to see how many times the required number of beads "goes into" the available number of beads.
Silver: 8160/85 = 96
Black: 2880/30 = 96
Camilla has enough beads to make 96 necklaces.
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Comment on this answer
Obviously, if one of the quotients is smaller than the other, Camilla can only make as many necklaces as are supported by the constraining resource.
Even if she had 3000 black beads (way more than 2880), she could still only make 96 necklaces (for example) because she would run out of silver beads making that 96th necklace. (There would be 120 black beads left over in that scenario.)