Final answer:
The value of integer d is 21. This is found by first calculating the total sum of the integers, given the mean, and then subtracting the sum of a, b, and c from this total.
Step-by-step explanation:
To find the value of d, we first need to understand that the mean of a set of numbers is the sum of the numbers divided by the amount of numbers. Given that the mean of a, b, c, and d is 15, we can set up the equation to find the total sum:
(a + b + c + d) / 4 = 15
Therefore:
a + b + c + d = 15 x 4
a + b + c + d = 60
We are also told that the sum of a, b, and c is 39. Subtracting this sum from the total gives us:
60 - 39 = d
This means d equals 21.