Since, c varies directly as n, the cost of the sandwiches when n equals to 3 is 18.
Variation is defined by any change in some quantity due to change in another.
Therefore,
c ∝ n
c = kn
where
Therefore,
54 = 9k
k = 54 / 9
k = 6
Therefore, when n = 3 , c = ?
c = 6 × 3
c = 18
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