Tautology and Inference

$($a$)$ Prove using propositional logic laws, that the inference below is valid.

$\frac{p^{{?}^{?}}q,pr}{q^{{?}^{?}}r}$

$($b$)$ Using inference rules, show that we can infer $q^{{?}^{?}}r$ from the premises $p^{{?}^{?}}q$ and $pr.$