Answer
$\displaystyle \frac{x+3}{2}$
Work Step by Step
To add rational expressions with the same denominator,
add numerators and place the sum over the common denominator.
If possible, factor and simplify the result.
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$\displaystyle \frac{x-3}{12}+\frac{5x+21}{12} = \displaystyle \frac{x-3+5x+21}{12}$
= $\displaystyle \frac{6x+18}{12}$
= $\displaystyle \frac{6(x+3)}{6(2)}\qquad$... reduce by 6
= $\displaystyle \frac{x+3}{2}$
