Q.If $\binom{20}{r-1} + 2 \binom{20}{r} + \binom{20}{r+1} = \dfrac{21}{22} \binom{21}{r} \cdot k$ , then $k$ is

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Q.If (20r−1)+2(20r)+(20r+1)=2122(21r)⋅k\binom{20}{r-1} + 2 \binom{20}{r} + \binom{20}{r+1} = \dfrac{21}{22} \binom{21}{r} \cdot k(r−120​)+2(r20​)+(r+120​)=2221​(r21​)⋅k, then kkk is