The position vector of a pointis r=x î+y ĵ+z k̂, where x, y, z ∈ N and 𝐚=𝐢̂+2 𝐣̂+𝐤̂. If r ·𝐚...

The position vector of a pointis r=x î+y ĵ+z k̂, where x, y, z ∈ N and 𝐚=𝐢̂+2 𝐣̂+𝐤̂. If r ·𝐚=20, then the number of possible position of P is
(a) 81
(b) 49
(c) 100

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