STEP 1: find angle $ \alpha $
To find angle $ \alpha $ use formula:
$$ \sin \left( \frac{ \alpha }{ 2 } \right) = \dfrac{ d_2 }{ d_1 } $$After substituting $ d_2 = 42 $ and $ d_1 = 56 $ we have:
$$ \sin \left( \frac{ \alpha }{ 2 } \right) = \dfrac{ 42 }{ 56 } $$ $$ \sin \left( \frac{ \alpha }{ 2 } \right) = \frac{ 3 }{ 4 } $$ $$ \frac{ \alpha }{ 2 } = \arcsin\left( \frac{ 3 }{ 4 } \right) $$ $$ \frac{ \alpha }{ 2 } = 48.5904^o $$$$ \alpha = 48.5904^o \cdot 2 $$$$ \alpha = 97.1808^o $$STEP 2: find height $ h $
To find height $ h $ use formula:
$$ \sin \left( \frac{ \alpha }{ 2 } \right) = \dfrac{ h }{ d_1 } $$After substituting $ \alpha = 48.5904 $ and $ d_1 = 56 $ we have:
$$ \sin \left( \frac{ 97.1808^o }{ 2 } \right) = \dfrac{ h }{ 56 } $$ $$ \sin( 48.5904 ) = \dfrac{ h }{ 56 } $$ $$ 0.75 = \dfrac{ h }{ 56 } $$$$ h = 0.75 \cdot 56 $$$$ h = 42 $$