STEP 1: find height $ h $
To find height $ h $ use formula:
$$ \sin \left( \frac{ \beta }{ 2 } \right) = \dfrac{ h }{ d_2 } $$After substituting $ \beta = 80^o $ and $ d_2 = 13542 $ we have:
$$ \sin \left( \frac{ 160^o }{ 2 } \right) = \dfrac{ h }{ 13542 } $$ $$ \sin( 80^o ) = \dfrac{ h }{ 13542 } $$ $$ 0.9848 = \dfrac{ h }{ 13542 } $$$$ h = 0.9848 \cdot 13542 $$$$ h = 13336.2666 $$STEP 2: find incircle radius $ r $
To find incircle radius $ r $ use formula:
$$ h = 2 \cdot r $$After substituting $ h = 13336.2666 $ we have:
$$ 13336.2666 = 2 \cdot r $$ $$ r = \dfrac{ 13336.2666 }{ 2 } $$ $$ r \approx 6668.1333 $$