$(4)$ Two $C1550$ are to be used as a structural member as shown in figure. Determine the distance $"$L$"$ separating them $($web$-$to$-$web clear distance$)$ so that the moment of inertia about the centroidal $y-$axis is equal to the moment of inertial about the centroidal $x-$axis. Properties of $C1550$ are tabulated below.

Properties of $C1550$

$\backslash$table$[[\backslash$table$[[$Area$],[(m{m}^2)$