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Let a r = i ˆ + j ˆ 4 + k ˆ 2 , b r = i ˆ 3 – j ˆ 2 + k ˆ 7 and c r = j ˆ – i ˆ 2 + k ˆ 4 . If a vector d r satisfies b d r r × = b c r r × and a d r r ⋅ = 24, then 2 | d | r is equal to

1. 323
2. 423
3. 313
4. 413

Correct answer: 413

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