Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Time | Show Name | Local/Networked | Ad Freq | News Freq |
| --- | --- | --- | --- | --- |
| 6:00am–9:00am | Truckin' With Tim | Networked | 20 Minutes | 60 Minutes |
| 9:00am–12:00am | American Top 40 | Pre-Recorded | 20 Minutes | 60 Minutes |
| 12:00pm–6:00pm | AFL | Networked | During quarters | N/A |
| 6:00pm–7:00pm | Classic Vinyl | Pre-Recorded | 20 minutes | 60 minutes |
| 7:00pm–9:00pm | My Generation | Pre-Recorded | 20 Minutes | 60 Minutes |
| 9:00pm–12:00am | Classic Hits | Local | 20 Minutes | 60 Minutes |
Question:
How often are there ads during American Top 40?
Answer:
20 Minutes