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In this kind of simplification, you always simplify out by using the common factor in the expression. In this case for 4x+3, there is no common factor that can be used to divide both 4x and 3. It would have been possible if the term was 4x+4 as 4 would have been a common factor and thus giving 4(x+1) but for the case of 4x+3, that answer is simplified and nothing more can be done about it.
opening the brackets
putting like terms together
thus the answer reduces to zero
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