Unpolarized light of intensity i0nbspis sent through 4

Question

Unpolarized light of intensity I₀ is sent through 4 polarizers, each of the last three rotated 30^o from the previous polarizer so that the last polarizer is perpendicular to the first. What is the intensity transmitted by this system?

1) 0.75 I₀

2) 0.50 I₀    

3) 0.42 I₀

4) 0.21 I₀

5) 0.00