Start by setting up a factor tree for 4 and 3.
4 factors as 2 · 2 and 3 doesn't factor.
When finding the least common multiple, we are looking for factors that match up and notice that we have no factors in common.
In this situation, the least common multiple
comes from multiplying them together.
So we have 4 · 3 or 12 which means the lcm of 3 and 4 is 12.
I have also shown my work below.