Janice is correct for disagreeing with Eliza as Eliza is wrong in stating that 30 is the only multiple of 3 that is also a multiple of 10.
The Breakdown
To determine if a number is a multiple of both 3 and 10, we need to find the common factors of these two numbers.
The multiples of 3 are: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ...
The multiples of 10 are: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, ...
As we can see, there are multiple numbers that are both multiples of 3 and 10. In addition to 30, we have 60 and 90 as well.