Answer
$\color{blue}{\dfrac{4}{a-2}}$
Work Step by Step
Factor out $-1$ in the denominator of the subtrahend to obtain:
$=\dfrac{3}{a-2} - \dfrac{1}{-1(-2+a)}
\\=\dfrac{3}{a-2} - \dfrac{-1}{a-2}$
The expressions are similar so subtract the numerators and copy the denominator to obtain:
$=\dfrac{3-(-1)}{a-2}
\\=\dfrac{3+1}{a-2}
\\=\color{blue}{\dfrac{4}{a-2}}$
