To determine how many calls each volunteer has to make, we can start with the total number of calls (280) and the total number of volunteers.
There are 4 groups of 7 volunteers each:
Total number of volunteers = 4 groups × 7 volunteers/group = 28 volunteers
Now we can calculate how many calls each volunteer needs to make by dividing the total number of calls by the total number of volunteers:
Calls per volunteer = Total calls / Total volunteers = 280 calls / 28 volunteers = 10 calls per volunteer
So, each volunteer needs to make 10 calls to reach the goal.