Exercice in cross correlation

Help me finding the answers, I can’t do it alone.
Given v (t) = Rectλ/2 and x (t) = sin βt, with β = 2π/T
a) evaluate the cross-correlation rvx (t) of the two signals v (t) and x (t).
b) Under what condition would the cross-correlation rvx (t) be nil?