The LCM is the lowest common multiple, this means the smallest number that 6, 4 and 10 can go into without giving a decimal number, so they give an integer.
Here's a trick, use prime factorization
Prime factorization means, write a number as the result of the multiplication of prime numbers
prime numbers are numbers with only two factors, 1 and itself
So the prime factorization of 6, 4 and 10 is
6 = 2 x 3
4 = 2 x 2
10 = 2 x 5
For each prime factor, find where it occurs most often as a factor and write it that many times in a new list.
So 2 occurs most often as a factor of 4, so we use two 2s
3 occurs most often as a factor of 6, so we use one 3
5 occurs most often as a factor of 10, so we use one 5
