You have already invested $550 in a stock with an annual return of 11%. How much more should be invested at 15% so that the return on the total investment is 12%?

Let x be the additional amount invested at 15%. The total investment must earn 12%, so 0.11(550) + 0.15x = 0.12(550 + x). Rearranging gives 0.03x = 5.50, so x = $183.33. The additional investment should be $183.33, choice A.

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