Final answer:
Seth earned $284.55 last week by selling 21 candles at $14.35 each, after subtracting the material costs of $16.80.
Step-by-step explanation:
To calculate Seth's earnings from selling candles last week, we need to first determine the total sales and then subtract the cost of materials. Seth sold 21 candles for $14.35 each. The total sales amount to 21 candles × $14.35 per candle = $301.35. Next, we'll calculate the cost of materials. Since Seth pays $2.40 for every 3 candles, the cost for 21 candles is (21 candles / 3 candles) × $2.40 = 7 × $2.40 = $16.80.
To find Seth's earnings, we subtract the total cost of materials from the total sales: $301.35 - $16.80 = $284.55. Therefore, Seth earned $284.55 last week from selling candles.