w(2w-1)=21

$$\\w(2w-1)=21\\
2w^2-w-21=0\\
2w^2+6w-7w-21=0\\
2w(w+3)-7(w+3)=0\\
(2w-7)(w+3)=0\\
w=7/2 \;\;or\;\;w=-3$$

 

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w=21

or 2w-1=21    2w=22    w=11