First, find the mean. You'll need it to compute the variance.

The variance of the sample is then computed with the formula

The standard deviation is the square root of the variance, so
Answer:
c = 1.5 d
Step-by-step explanation:
cost of 4 small drinks = $6
cost of 1 small drink = $
= $1.5
cost of d small drinks = 1.5 d = c
∴ c = 1.5 d
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