Brainliest rewarded to correct answer mickey simplified the expression below. he then checked his work by substituting 4 for x. he noticed his two values were not equal. what was mickey’s error when simplifying? expression: 2x^2 - 4x - 9 - x^2 + 2x + 3 simplified expression: x^2 - 6x - 6 answer choices: mickey should have added –4 and 2 when combining the coefficients of the x terms. mickey should have added 2 and 1 when combining the x^2 terms. mickey should have added 9 and 3 when combining the constant terms. mickey should have added –4 and –1 when combining the x terms.