In a physics demonstration, two long parallel wires are separated by a distance of 2.80 cm. One wire carries a current of 1.40 A while the other carries a current of 3.40 A. The currents are in the same direction.(a)What is the magnitude of the force per unit length (in N/m) that one wire exerts on the other?

I got ...(4*pi*10^-7)(1.40)(3.40)/2*pi(2.80*10^-2) = 3.399*10^-4

but that is not correct what did i do wrong?