Infinite hollow cylinder

Find the magnetic field at the horizontal distance of $2\text{ m}$ from the center of a horizontal infinite hollow cylinder of inner radius $1\text{ m}$ and outer radius $3\text{ m}$ .

$I_\text{current} = \dfrac1{\mu_0} \text{ ampere}$ .

If your answer as $\dfrac ab \pi$ , where $a$ and $b$ are coprime positive integers, submit $a+b$ .