find all the prime factors of the three numbers. pick up the common factors, ONCE, then pick up the non-common factors one by one, multiply the factors, the product is the least common factor.
example: the least common multiple of 6, 8, and 15
6=2*3
8=2*2*2
15=3*5
Note: do not write 8 into 4*2, because 4 is not a prime number. you have to break the number down to prime factors only.
Notice that 6 and 8 have a common factor 2, so pick up the 2;
6 and 15 have a common factor of 3, so pick up the 3.
those are the only two shared factors, so 2×3
now pick up whatever is not shared:
the two 2s for 8 and the 5 for 15 is not shared, add 2, 2, and 5 to the multiplication: 2×3×2×2×5=120
120 is the least common multiples of 6,8, and 15
this is basically how it is done. I believe you can explain better in your own words.