Question 1073089
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You are on the right way:

L + S = 16      (1)   (large candles and small candles)
7L + 3S = 76    (2)   (dollars).

Express L = 16 - S from (1) and substitute it into (2), replacing L.
You will get a single equation for S:

7*(16-S) + 2S = 76.


Can you complete on your own from this point ?
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This method is called the <U>"Substitution Method"</U>.