In the simple AC circuit shown,

In the simple AC circuit shown, R = 70.0 ohms and v = Vmax sin(wt)
a) if Vr = 0.250Vmax for the frst time at t = 0.0100 s, what is the angular frequency of the source?
b) what is the driving frequency of the AC source?
c) What is the next value of t for which Vr = 0.250Vmax