Explanation:

- The highest common factor (HCF) of the two numbers is given as 6.

- The product of the two numbers is provided as 72.

- The key relationship here is $\text{HCF}\times \text{LCM}=\text{Product of the numbers}$.

- Plugging the given values, we have $6\times \text{LCM}=72$.

- Solving for LCM gives $\text{LCM}=72/6=12$.

- Therefore, the least common multiple (LCM) of the two numbers is 12.

- Option:1, 16

- Incorrect because 6 multiplied by 16 does not give 72.

- Option:2, 18

- Incorrect because 6 multiplied by 18 does not give 72.

- Option:3, 12

- This is correct as 6 multiplied by 12 equals 72.

- Option:4, 14

- Incorrect because 6 multiplied by 14 does not give 72.