Answer: There’s technically no answer to this question, unless you specify that the zoo only has monkeys and elephants. If the zoo has more than two types of animal then the ratio doesn’t help because there are unknown variables.
However, if we knew that the zoo only has monkeys and elephants, then:
E = number of elephants
M = number of monkeys
M=9E
M + E = 60
9E+E= 60
10E = 60
E = 6
There are 6 elephants (and 54 monkeys).