Current Attempt in Progress

Your answer is incorrect.

If aligned and continuous carbon fibers with a diameter of $2\mathrm{.}90$ micron are embedded within an epoxy, such that the bond strength across the fiber$-$epoxy interface is $25$ MPa $,$ and the shear yield strength of the epoxy is $66$ MPa $,$ compute the minimum fiber length, in millimeters, to guarantee that the fibers are conveying an optimum fraction of force that is applied to the composite. The tensile strength of these carbon fibers is $3900$ MPa $.$

$l_c$ mm