Force between Two Parallel Currents: the Ampere

Find the force per unit length on two parallel current carrying current. 

Two long and parallel straight wires A and B carrying currents of $8.0 \mathrm{A}$ and $5.0 \mathrm{A}$ in the same direction are separated by a distance of $4.0 \mathrm{cm}$. Estimate the force on a $10 \mathrm{cm}$ section of wire A.