[tex] \triangle ABD\sim\triangle CAD\ \text{therefore the sides of triangles are in proportion}\\\\\dfrac{x}{12}=\dfrac{12}{27}\ \ \ |cross\ multiply\\\\27x=144\ \ \ |:27\\\\x=\dfrac{144}{27}\\\\x=\dfrac{16}{3}\\\\\boxed{\text{Answer:}\ B.\ \dfrac{16}{3}} [/tex]
