Final answer:
The value of f after substituting d = 15 in the given equation is 7.
Step-by-step explanation:
To find the value of f when d = 15, we substitute d = 15 into the expression for f:
f = d/3 + 2.
Plugging in d = 15 gives us:
f = 15/3 + 2
= 5 + 2
= 7.
Therefore, when d = 15, the value of f is 7.