Question 935669
We'll denote the measure of angle X as 

{{{m(X)}}}

In any triangle the sum of the angles is 180 degrees, so
{{{m(P)+m(Q)+m(O)=180}}}

so we know

{{{m(O)=180-(m(P)+m(Q))=180-89=91}}}

Now using the Law of Sines we write:


{{{
p/sin(80)=(870)/(sin(91))
}}}


which leads to 

{{{p=856.9}}}