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 Simplified Expression 2 x squared minus 4 x minus 9 minus x squared + 2 x + 3 x squared minus 6 x minus 6 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 squared 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. Mark this and return