Magnetic Force

A straight wire carries a current of 30 A in the north direction. Find the magnetic field 3.0 m directly below the wire.

How do magnets work?

Two long straight parallel wires are separated by a distance of 25 cm. One is carrying a current of 2 A, the other 4 A (the currents are aimed in the same direction) . What is the magnetic field, $\vec{B}$ at a point directly in the middle of the wires?

Three long wires parallel to the x axis carry currents as shown below. If I = 20 A, what is the magnetic field at the origin (magnitude and direction) ?