Solve this following
Question:

If $\overrightarrow{\mathrm{a}}$ and $\overrightarrow{\mathrm{b}}$ are two unit vectors such that $|\overrightarrow{\mathrm{a}}+\overrightarrow{\mathrm{b}}|=\sqrt{3}$, find $(2 \overrightarrow{\mathrm{a}}-5 \overrightarrow{\mathrm{b}}) \cdot(3 \overrightarrow{\mathrm{a}}+\overrightarrow{\mathrm{b}})$.

Solution: