9514 1404 393
Answer:
14 units
Explanation:
The angle bisector divides the sides proportionally, so you have ...
(x+4)/8 = (2x+1)/12
3(x +4) = 2(2x +1) . . . . . . multiply by 24
3x +12 = 4x +2 . . . . . . . . eliminate parentheses
10 = x . . . . . . . . . . . subtract (3x+2)
Then BD = x+4 = 10 +4.
The length of BD is 14 units.
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Additional comment
The "triangle" cannot exist, as the side lengths are shown as 8, 12, and 35. The long side is too long. Nice math; bad geometry.