The problem statement implies that TK and DK are segments related to a triangle, likely with point T and D being on sides or extensions of sides of a larger triangle. The condition TK = DK suggests that K is the midpoint of some segment, or that triangle TDK is isosceles. The right angle at T on FK and at D on BK are also important clues. However, without more information or a clearer diagram indicating which triangles are similar or what specific geometric properties apply, it is impossible to provide a definitive numerical answer. The given information is insufficient to solve for FT. If we assume that FK is parallel to BK and that T and D are points on FK and BK respectively, and that FT is a segment of FK, and BD is a segment of some other line, then more information about the configuration is needed.
Without additional context or clarification on the geometric relationships between points F, T, K, B, and D, and the specific properties of the triangles formed, a precise calculation for the length of FT cannot be performed.