To find hypotenuse $ c $ use formula:
$$ \sin \left( \beta \right) = \dfrac{ b }{ c } $$After substituting $ \beta = 60^o $ and $ b = 4 \sqrt{ 3 } $ we have:
$$ \sin( 60^o ) = \dfrac{ 4 \sqrt{ 3 } }{ c } $$ $$ \frac{\sqrt{ 3 }}{ 2 } = \dfrac{ 4 \sqrt{ 3 } }{ c } $$ $$ c = \dfrac{ 4 \sqrt{ 3 } }{ \frac{\sqrt{ 3 }}{ 2 } } $$ $$ c = 8 $$