Magnetic Flux Questions

A circular disc of radius $0.2\text{meter}$ is placed in a uniform magnetic field of induction $\frac{1}{\pi }{\text{Wb/m}}^2$ in such a way that its axis makes an angle of $60^{\circ }$ with $\vec{B}$. The magnetic flux linked with the disc is:

A long solenoid has $500$ turns. When a current of $2\text{ampere}$ is passed through it, the resulting magnetic flux linked with each turn of the solenoid is $4\times 10^{-3}\text{Wb}$. The self-inductance of the solenoid is:

A coil of resistance $400\Omega$ is placed in a magnetic field. If the magnetic flux $\varphi$ (Wb) linked with the coil varies with time $t$ (s) as $\varphi =50t^2+4$, the current in the coil at $t=2\text{s}$ is: