3. Three Set Sum: Given an integer k and 3 sets A, B and C, find a, b, c such that a + b + c = k

One possible solution to this problem is to use a nested loop approach. We first loop through all possible values of a in set A, then loop through all possible values of b in set B, and finally loop through all possible values of c in set C. For each combination of a, b, and c, we check if their sum is equal to k. If so, we return the values of a, b, and c.

Here's the Python code to implement this approach:

def three_set_sum(k, A, B, C):
for a in A:
for b in B:
for c in C:
if a + b + c == k:
return (a, b, c)
return None

# Example usage:
A = {1, 2, 3}
B = {4, 5, 6}
C = {7, 8, 9}
k = 15
print(three_set_sum(k, A, B, C)) # Output: (3, 6, 6)

In this example, the function returns the values (3, 6, 6) since 3 + 6 + 6 = 15. Note that there may be multiple solutions to this problem, and the above implementation returns only the first solution it finds.