Answer:
C. 6
Step-by-step explanation:
ΔADC and ΔACB are similar because two of their angles are congruent (∠ACD and ∠ABC, and ∠DAC and ∠CAB)
Because the sides are similar, you can create a proportion
[tex]\frac{AC}{AD}=\frac{AB}{AC}[/tex]
substitute the given values for the sides. AD=4 and AB=4+5=9
[tex]\frac{AC}{4}=\frac{9}{AC}[/tex]
cross multiply
[tex]AC^{2} =36[/tex]
take the square root of both sides
AC=6
