amplitude, perodic time, angular velocity, phase angle and lead time!

i am working through a question, and just wanted to make sure i am on the right lines. so guidence and help be great the question is as follows:

an oscillating mechanism has a maximum displacement, d of 1.6m and a freqency of 20Hz. At a time t=0 sec the displacement is +50 cm.

determine the amplitude, periodic time, angular velocity, phase angle and lead time, then express the displacement in the form Rsin (vt + a)

my working:

amplitude A = maximum displacement

A = 1.6m

angular velocity: omega symbol = 2pf

=2pf 20Hz

= 40prad/sec

phase angle, x use displacement, d = A sin (v t + a)

d = 1.6sin (40pt+a)

when t=0, d =0.50m

0.50=1.6sin(40p(0)+a)

0.50=1.6sin(a)

0.50/1.6=sin a

sin-1 0.50/1.6 = a

=18.2 degress

18.2 x p rads/180

a=18.2 x p rads/180

a= 0.317rad

displacement = 1.6sin(40p (t) + 0.317)

=1.6 (40t+0.317)

this is where i get bit lost, to get to the lead time. i know the formula a/v

any help to get there by great thanks