Of the 50 employees of a certain company, 30 earn an average (arithmetic mean) salary of $30,000, 15 earn an average salary of $40,000, and 5 earn an average salary of $60,000. What is the average salary earned by the employees of this company?
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A $30,000
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B $36,000
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C $40,000
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D $45,000
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E $50,000