To determine how long it will take to complete the project with 5 people working on it, you can use the formula:
\[ \text{Time (in days)} = \frac{\text{Total person-days}}{\text{Number of people}} \]
Given that the total person-days to complete the project is 720 and there are 5 people working, the calculation will be:
\[ \text{Time} = \frac{720 \text{ person-days}}{5 \text{ people}} = 144 \text{ days} \]
Therefore, it will take 144 days to complete the project with 5 people working on it.