#### Answer

$S=9pq$

#### Work Step by Step

Since $S$ is jointly proportional to $p$ and $q$, we have:
$S=kpq$
We are given: $S=180$ and $p=4$ and $q=5$, so we have:
$180=k*4*5$
$180=20*k$
$k=180/20=9$
So the equation is:
$S=9pq$

Published by
Brooks Cole

ISBN 10:
1305115546

ISBN 13:
978-1-30511-554-5

$S=9pq$

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