To find angle $ \beta $ use formula:
$$ \tan \left( \beta \right) = \dfrac{ b }{ a } $$After substituting $ b = \sqrt{ 33 } $ and $ a = \sqrt{ 39 } $ we have:
$$ \tan \left( \beta \right) = \dfrac{ \sqrt{ 33 } }{ \sqrt{ 39 } } $$ $$ \tan \left( \beta \right) = \frac{\sqrt{ 143 }}{ 13 } $$ $$ \beta = \arctan\left( \frac{\sqrt{ 143 }}{ 13 } \right) $$ $$ \beta = 42.6099^o $$