to bisect something, simply means to cut it into two equal halves.
so YU is an angle bisector, meaning ∡ZYU and ∡UYW are twins, meaning 8p - 10 = 10p -20.
[tex] \bf 8p-10=10p-20\implies -10=2p-20\implies 10=2p\implies \cfrac{10}{2}=p\\\\\\5=p ~\hspace{15em} \stackrel{\measuredangle ZYU}{8(5)-10}\implies 30 [/tex]
