The problem
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how does the -4b become +4b in the second last step
Answer provided by our tutors
There is a negative sign in front of the expression, that is, we have "-(4a - 4b)".
We want to get rid of the parentheses, and this is the same as multiplying each term by (-1):
-(4a - 4b) = (-1)(4a - 4b) = (-1)*(4a) + (-1)(-4b) = - 4a + 4b
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