To find the unit rate of push-ups per day, you need to divide the total number of push-ups by the total number of days:
\[ \text{Unit rate} = \frac{\text{Total push-ups}}{\text{Total days}} = \frac{280 \text{ push-ups}}{14 \text{ days}} = 20 \text{ push-ups per day} \]
So, the unit rate is 20 push-ups per day.