To find angle $ \beta $ use formula:
$$ \cos \left( \beta \right) = \dfrac{ a }{ c } $$After substituting $ a = 7 $ and $ c = 16 $ we have:
$$ \cos \left( \beta \right) = \dfrac{ 7 }{ 16 } $$ $$ \cos \left( \beta \right) = \frac{ 7 }{ 16 } $$ $$ \beta = \arccos\left( \frac{ 7 }{ 16 } \right) $$ $$ \beta = 64.0555^o $$