If $\sin \theta-\cos \theta=\frac{4}{5}$, then find the value of $\sin \theta+\cos \theta$.

$\frac{5}{\sqrt{34}}$ $\frac{5}{\sqrt{24}}$ $\frac{\sqrt{34}}{5}$ $\frac{\sqrt{24}}{5}$

$\frac{\sqrt{34}}{5}$