Line segment bd passes through the center of circle c, bh = a, and hd = 8. what is the length of the diameter?

If the line down the center is 8 and the diaameter is in the middle then both those sides need to be 8 and so the 6's on both sides of the diameter have to stay they same but they only change a little for 6+6 is 12 but the length gets longer since it moved farther down 
answer D 12.5

We need more info then that