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Let → a = 2 i ˆ – j ˆ + 3 k ˆ , → b = 3 i ˆ – 5 j ˆ + k ˆ and → c be a vector such that → a × → c = → c × → b and ( → a + → c ).( → b + → c ) = 168. Then the maximum value of 2 c → is :

1. 77
2. 462
3. 308
4. 154

Correct answer: 308

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