Two parallel conductors carrying current of 4.0 A and 10.0 A are placed 2.5 cm apart in vacuum. The force per unit length between them is
(a) 6.4 x 10-5 N/m
(b) 6.4 x 10-2 Nm
(c) 4.6 x 10-4 N/m
(d) 3.2 x 10-4 N/m 84102, 841152