Open Question: I made an investment of $6000 at an annual simple interest rate of 5.5%?

I made an investment of 6000 at an annual simple interest rate of 5.5%. How much additional money must she invest at an annual simple interest rate of 10% in order for the total annual interest earned to be 7% of the investment?
I can't quite set up the equation.

6000(.055) + .10x = (6000[.055] + .10x)(.07)?

Please help

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