Solve for u
u=12
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-21\left(-\frac{4}{7}\right)=u
Multiply both sides by -\frac{4}{7}, the reciprocal of -\frac{7}{4}.
\frac{-21\left(-4\right)}{7}=u
Express -21\left(-\frac{4}{7}\right) as a single fraction.
\frac{84}{7}=u
Multiply -21 and -4 to get 84.
12=u
Divide 84 by 7 to get 12.
u=12
Swap sides so that all variable terms are on the left hand side.
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