Answer
P : $B = 0$
R : $B = \mu_0 nI$
S : $B = 0$
Work Step by Step
The sheet above is number 1 and the other one is number 2.
At each point, $\vec{B} = \vec{B}_1 + \vec{B}_2$
P : $\vec{B}_1$ and $\vec{B}_2$ have different directions. $B = -\mu_0 \frac{nI}{2} + \mu_0 \frac{nI}{2} = 0$
R : $\vec{B}_1$ and $\vec{B}_2$ have the same direction. $B = 2\mu_0 \frac{nI}{2}$
S : $\vec{B}_1$ and $\vec{B}_2$ have different directions. $B = 0$
