Here's the question you clicked on:
woleraymond
What is the magnetic flux density midway between two long parallel wires separated by 10 cm each carrying a current of 5A. a - In the same direction b- In opposite direction What is the force per unit length exerted by each wire on the other?
You now need \[B = \frac{\mu_{o} I}{2 \pi r} \] where r is the distance from the wire.
For the last part you can look at this: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.html#c1 (this website is great for looking things up, though the correct page is usually easiest to find using the method of searching google for "#what you want# hyperphysics"