Respuesta :

Answer:

B

Step-by-step explanation:

AD is an angle bisector and divides the opposite sides into segments that are proportional to the other 2 sides , that is

[tex]\frac{AC}{AB}[/tex] = [tex]\frac{CD}{BD}[/tex] , substitute values

[tex]\frac{12}{21}[/tex] = [tex]\frac{4}{BD}[/tex] ( cross- multiply )

12 BD = 84 ( divide both sides by 12 )

BD = 7 → B

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