Respuesta :

calculista
we know that
B=72º58'=72+58/60----> 72.97°
A=50º12'=50+12/60----> 50.2°
C=180-(72.97+50.2)----> C=56.83°
applying the law of sines
b/sin B=c/sin C--------> b=c*sin B/sin C----> b=12*sin 72.97/sin 56.83
b=13.71-----> b=14

the answer is
b=14