6. The values of $p$ which satisfy the equations
$$
\begin{aligned}
p^{2}+9 q^{2}+3 p-p q & =30 \\
p-5 q-8 & =0
\end{aligned}
$$
may be found by solving
(a) $x^{2}-x-6=0$;
(b) $13 x^{2}-121 x-426=0$;
(c) $29 x^{2}-101 x-174=0$;
(d) $29 x^{2}+115 x-1326=0$;
(e) $39 x^{2}-104 x-174=0$.
6 Ans: (a).
Substituting $q=\frac{1}{5}(p-8)$ into the first equation, we get (a)