When the diagonals of a quadrilateral are perpendicular, the area of that quadrilateral is half the product of their lengths.
.. A = (1/2)*d₁*d₂
Substituting the given information, this becomes
.. 58 in² = (1/2)*(14.5 in)*d₂
.. 2*58/14.5 in = d₂ = 8 in
The length of diagonal BD is 8 in.