To find out how many calls each volunteer has to make, you can follow these steps:
- Total Calls: 280
- Total Volunteers: 4 groups × 7 volunteers = 28 volunteers
Now, divide the total number of calls by the total number of volunteers:
\[ \frac{280 \text{ calls}}{28 \text{ volunteers}} = 10 \]
So, each volunteer has to make 10 calls to reach the goal.
The correct response is 10.