To find an LCM you must know the factors. So we start by factoring:
The LCM is the product of all these factors using the highest exponent on each common factor:
Note that the common factors, 5 and (x+3), were used only once. If, for example, we had had (x+3)^2 in one factorization and (x+3) in the other, then we would use (x+3)^2 (the higher exponent) in the LCM.