What is the smallest common multiple of 4, 5, and 6? __________.​

Let us write the multiples of 4, 5, and 6 in the circles and their common multiples in the common spaces accordingly.
<write the multiples of 4, 5 and 6 as shown below>

Thus, the smallest common multiples of 4, 5, and 6 is 60.
Here, we could have gone beyond 60 for every number as you know that multiples can be infinite in numbers.
But let us keep the numbers till 60 only for simplicity.