r/-5=10
s/6=54
-30=t/20
As always, we wish to get the variable by itself:
$\displaystyle \frac{s}{6} = 54$
$\displaystyle 6 \cdot \frac{s}{6} = 6 \cdot 54$
$\displaystyle s = 324$
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$\displaystyle -30 = \frac{t}{20}$
$\displaystyle 20 \cdot (-30) = 20 \cdot \frac{t}{20}$
$\displaystyle -60 = t$
-Dan