To find leg $ b $ use formula:
$$ \sin \left( \beta \right) = \dfrac{ b }{ c } $$After substituting $ \beta = 74^o $ and $ c = 20 $ we have:
$$ \sin( 74^o ) = \dfrac{ b }{ 20 } $$ $$ 0.9613 = \dfrac{ b }{ 20 } $$$$ b = 0.9613 \cdot 20 $$$$ b = 19.2252 $$