Right answer is (b) Vt L0 / ns
Easy explanation: Battens should be designed to resist longitudinal shear equal to V = Vt L0 / ns , where Vt is transverse shear force, L0 is distance between centre-to-centre of battens longitudinally, s is minimum transverse distance between centroids of bolt/rivet group/ welding connecting batten to main member, n is number of parallel planes of battens.