![\huge\text{$m\angle O=\boxed{11^(\circ)}$}](https://img.qammunity.org/2021/formulas/mathematics/high-school/npt9sos5m9m74d356nvzmrtd9a9u659wte.png)
Since we know that all angles in a triangle add up to
, we can solve for
and substitute it back into
to find
.
![\begin{aligned}m\angle N+m\angle O+m\angle P&=180\\(5x-8)+(x-5)+(6x+1)&=180\end{aligned}](https://img.qammunity.org/2021/formulas/mathematics/high-school/k4r41z29uat5p8ffvwjrq2opnccdgurshx.png)
Remove the parentheses and combine like terms.
![\begin{aligned}5x-8+x-5+6x+1&=180\\(5x+x+6x)+(-8-5+1)&=180\\12x-12&=180\end{aligned}](https://img.qammunity.org/2021/formulas/mathematics/high-school/ys7xifpo1osmo8vi50m54cx3buww0q25pl.png)
Add
to both sides of the equation.
![\begin{aligned}12x-12&=180\\12x&=192\end{aligned}](https://img.qammunity.org/2021/formulas/mathematics/high-school/n2tieg3gdfj18l68p9hv7oy34eygn4fkhu.png)
Divide both sides of the equation by
.
![\begin{aligned}x=16\end{aligned}](https://img.qammunity.org/2021/formulas/mathematics/high-school/fdklbig2hb8h2sgn0bhlb8damt96btkhxv.png)
Now that we have the value of
, we can substitute it back into
to find
.
![\begin{aligned}m\angle O&=(x-5)\\&=16-5\\&=\boxed{11}\end{aligned}](https://img.qammunity.org/2021/formulas/mathematics/high-school/27trupej9lbv9mkwpxyg1f41dexmdskq6g.png)