Answer:
{2, 8}
Explanation:
We want to find x for ...
15 = 4|x -5| +3
12 = 4|x -5| . . . . subtract 3
3 = |x -5| . . . . . . divide by 4
±3 = x -5 . . . . . . show the meaning of absolute value
5 ±3 = x = {2, 8} . . . . . add 5
The values of x for which f(x) = 15 are 2 and 8.