4. A voltage wave on a transmission line is given by $v(z,t) = 8Sin(4\pi t - 10\pi z)$ where x is the distance from the source. What is (a) the direction of propagation? (b) the frequency f? (c) the Wavelength $\lambda$? and (d) the phase velocity? (e) Express v(x,t) as a phasor.