I've held off a bit, but you don't seem to be getting a lot of homework turned in :<) , so I won't try to hide this.

a = (.6 cos s, .6 sin s, .8 s).
T = a'/a = (-.6 sin s, .6 cos s, .8).
T' = (-.6 cos s, -.6 sin s, 0), so
κ = .6 and
N = (-cos s, -sin s, 0).  
B = T x N
   =  ( .48 sin s, -.48 cos s , .6)

B' = (.48 cos s, .48 sin s, 0 ) so

τ = .48