Calculate : Average Revenue and Marginal Revenue from the following given data:
| Total Sales (In Units) | 1 | 2 | 3 | 4 | | Total Revenue (In) | 20 | 36 | 48 | 56 |
| Average Revenue (AR) | 20 | 18 | 16 | 14 | | Marginal Revenue (MR) | 20 | 16 | 12 | 8 |