Theory of acids and bases

Consider a $0.050\;M$ solution of the weak base pyridine ($C_5H_5N$ , $K_b$ $=$ $1.7 \cdot 10^{-4}$) $C_5H_5N$ $+$ $H_2O$ $HC_5H_5N^+$ $+$ $OH^-$

We found: $[OH^-]$ $=$ $x$ $=$ $1,3\cdot 10^{-2} \;M$

How do we proceed now to calculate the $pH$ of this solution ?

a) $pH$ $=$ $- log [H_3O^+]$ b) $pOH$ $=$ $- log[OH^-]$, and then $pH$ $=$ $14-pOH$ c) $[H_3O^+]$ $=$ $\frac{K_e}{[OH^-]} $ , and then $pH$ $=$ $- log [H_3O^+]$ d) $[H_3O^+]$ $=$ $10^{-pH}$