Expand dot products using magnitudes and an angle

Given $|\mathbf a|=4$, $|\mathbf b|=5$ and the angle between $\mathbf a$ and $\mathbf b$ is $45^\circ$, find the exact values of the following:

(i) $\mathbf a\cdot\mathbf b$

(ii) $(4\mathbf a+2\mathbf b)\cdot(3\mathbf a-\mathbf b)$

(iii) $|\mathbf a-\mathbf b|^2$