To find leg $ b $ use formula:
$$ \tan \left( \alpha \right) = \dfrac{ a }{ b } $$After substituting $ \alpha = 76^o $ and $ a = 13 $ we have:
$$ \tan( 76^o ) = \dfrac{ 13 }{ b } $$ $$ 4.0108 = \dfrac{ 13 }{ b } $$ $$ b = \dfrac{ 13 }{ 4.0108 } $$ $$ b = 3.2413 $$