Ruby has a monthly salary of $1,800 and also earns 6% commission on her sales. If Ruby had $37,000 in sales last month, what were her total earnings for the month?

Ruby earns 6% of $37,000 in sales: 0.06 × $37,000 = $2,220. Add her $1,800 monthly salary to the commission: $1,800 + $2,220 = $4,020. Her total earnings were $4,020, choice D.

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