Which of the following gives the value of the magnetic field according to Biot-Savart's law?

Find the magnetic field at point $P$ in the given diagram. The wire carries a current $i$.

The magnetic field due to a current-carrying circular coil on its axis at a distance of $\sqrt{2} \,d$ from the centre of the coil is $B$. If $d$ is the diameter of the coil,then the magnetic field at the centre of the coil is: (in $B$)

$A$ thin ring of $10 \, cm$ radius carries a uniformly distributed charge. The ring rotates at a constant angular speed of $40 \pi \, rad \, s^{-1}$ about its axis,perpendicular to its plane. If the magnetic field at its centre is $3.8 \times 10^{-9} \, T$,then the charge carried by the ring is close to $\left( \mu_0 = 4 \pi \times 10^{-7} \, N/A^2 \right)$.

$A$ long straight wire carries a current of $\pi \, A$. The magnetic field due to it will be $5 \times 10^{-5} \, Wb/m^2$ at what distance from the wire? $[\mu_0 = \text{permeability of free space}]$

$A$ hairpin-like shape as shown in the figure is made by bending a long current-carrying wire. What is the magnitude of the magnetic field at point $P$,which lies at the center of the semicircle?