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.