Phase Difference Questions

An ac voltage is applied to a resistance $R$ and inductor $L$ in series. If $R$ and the inductive reactance are both equal to $3\Omega$, the phase difference between the applied voltage and the current in the circuit is:

Two waves are represented by the equations $y_1=a\sin (\omega t+kx+0.57)\text{m}$ and $y_2=a\cos (\omega t+kx)\text{m}$. The phase difference between them is:

Two points are located at a distance of $10\text{m}$ and $15\text{m}$ from the source of oscillation. The period of oscillation is $0.05\text{sec}$ and the velocity of the wave is $300\text{m/sec}$. What is the phase difference between the oscillations of the two points?

Two particles oscillate with same frequency and amplitude. They pass each other moving in opposite directions when displacement is half the amplitude. The phase difference is: