Mrs. Ming invested an amount of money in two accounts for one year. She invested some at 8% interest and the rest at 6% interest. Her total amount invested was $1,500. At the end of the year, she had earned $106.40 in interest. How much had Mrs. Ming invested in the account paying 6%?

Let x be the amount invested at 6%, so $1,500 − x was invested at 8%. The interest equation is 0.06x + 0.08($1,500 − x) = $106.40; simplifying gives $120 − 0.02x = $106.40, so x = $680. Mrs. Ming invested $680 in the account paying 6%, choice B.

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