Since $\frac{\sqrt{2}\left(3+\sqrt{3}\right)}{8}$ and $\frac{\sqrt{2}\left(3-\sqrt{3}\right)}{8}$ have the same denominator, add them by adding their numerators.
Since $\frac{\sqrt{2}\left(1+\sqrt{3}\right)}{8}$ and $\frac{5\sqrt{2}+\sqrt{6}}{8}$ have the same denominator, subtract them by subtracting their numerators.