To find angle $ \alpha $ use formula:
$$ \sin \left( \frac{ \alpha }{ 2 } \right) = \dfrac{ d_2 }{ d_1 } $$After substituting $d_2 = 16\, \text{cm}$ and $d_1 = 22\, \text{cm}$ we have:
$$ \sin \left( \frac{ \alpha }{ 2 } \right) = \dfrac{ 16\, \text{cm} }{ 22\, \text{cm} } $$ $$ \sin \left( \frac{ \alpha }{ 2 } \right) = \frac{ 8 }{ 11 } $$ $$ \frac{ \alpha }{ 2 } = \arcsin\left( \frac{ 8 }{ 11 } \right) $$ $$ \frac{ \alpha }{ 2 } = 46.6582^o $$$$ \alpha = 46.6582^o \cdot 2 $$$$ \alpha = 93.3165^o $$