Solve for k
k=3
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-21+2k=-5k
Combine k and -6k to get -5k.
-21+2k+5k=0
Add 5k to both sides.
-21+7k=0
Combine 2k and 5k to get 7k.
7k=21
Add 21 to both sides. Anything plus zero gives itself.
k=\frac{21}{7}
Divide both sides by 7.
k=3
Divide 21 by 7 to get 3.
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