add or subtract the following polynomials as indicated (5.9x to the 3rd power+3.4x to the 2nd power - 7)-92.9x to the 3rd power -9.6x to the 2nd power +3)

just line them up and combine like powers:

5.9x^3 + 3.4x^2 - 7
-(92.9x^3 -9.6x^2 + 3)
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-87x^3 + 13x^2 - 10