Correct Answer: 50
Explanation:
a + b + c 2 = a 2 + b 2 + c 2 + 2 a b + b c + c a
2 a b + b c + c a = a + b + c 2 - a 2 + b 2 + c 2 = 169 - 69 = 100 = a b + b c + c a = 50
