ExplanationTotal number of buttons used = 50 (30 +20).

Number of buttons that weighs x grams per button = 30

The total mass of buttons that weighs x grams per button = 30x.

Number of buttons that weighs x grams per button = 20

Total mass of buttons that weighs 80 grams per button = \(80 \times 20\) =

1600.

Total mass of 50 buttons = 30x + 160.

Average mass of buttons = \(\frac{30x + 160}{50}= \frac{3}{5}x + 32\).

Hence option D is correct.
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Sandy

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