Final answer:
To find the average of three numbers, add them up and divide by the number of numbers.
Step-by-step explanation:
To find the average of three numbers, you need to add them up and then divide the sum by the number of numbers (which in this case is 3). So for option A, you would add the three numbers and then divide the sum by 3. For example, if the three numbers are 4, 5, and 7, you would calculate the average as (4 + 5 + 7) / 3 = 5.33.