Since $\frac{a\left(a+2\right)\left(-a\right)\left(a-1\right)}{3\times 2}$ and $\frac{\left(-2a+3\right)\times 3\times 2}{3\times 2}$ have the same denominator, add them by adding their numerators.
Since $\frac{a\left(a+2\right)\left(-a\right)\left(a-1\right)}{3\times 2}$ and $\frac{\left(-2a+3\right)\times 3\times 2}{3\times 2}$ have the same denominator, add them by adding their numerators.