To find angle $ \gamma $ use Thw Law of Sines:
$$ \dfrac{ \sin( \alpha )} { a } = \dfrac{ \sin( \gamma )} { c } $$After substituting $a = 124$, $\alpha = 100^o$ and $c = 12$ we have:
$$ \dfrac{ \sin( 100^o )} { 124 } = \dfrac{ \sin( \gamma )} { 12 } $$ $$ \dfrac{ 0.9848 } { 124 } = \dfrac{ \sin( \gamma ) } { 12 } $$ $$ \sin( \gamma ) \cdot 124 = 0.9848 \cdot 12 $$ $$ \sin( \gamma ) \cdot 124 = 11.8177 $$ $$ \sin( \gamma ) = \dfrac{ 11.8177 }{ 124 } $$ $$ \sin( \gamma ) = 0.0953 $$ $$ \gamma = \arcsin{ 0.0953 } $$ $$ \gamma \approx 5.4688^o $$