The length of BC is (B) 12. 
To get the length, we must first find the angle of the triangle using the equation tan θ = opposite/adjacent then we can derive the equation for the angle as θ = 

 (

). the angle (θ) = 33.69006753. Since they are similar triangles, we can use the same equation to find the length of BC. BC = tanθ*BF; BC = 

 * 18 and finally we can get BC = 12.