The length of side AD that will allow the angle at B to be bisected is 3m, the correct option is D.
What is Angle Bisector Theorem?
According to the angle bisector theorem, the angle bisector of an angle of a triangle bisects the opposite side into two parts that are proportional to the other two sides.
The sides of the triangle are 5,7 and (x+4) m.
The BD will be the angle bisector of angle B only if
x/4 = 5/7
x = 5 *4 / 7
x = 20/7 = 2.85 ≈ 3m
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