Unpolarized Light of Intensity $I _ { 0 }$ Passes Through Four Ideal Polarizing Sheets

Short Answer

Unpolarized light of intensity $I _ { 0 }$ passes through four ideal polarizing sheets. The polarizing angle of each sheet is rotated $30 ^ { \circ }$ from the one before it, so that the last sheet is aligned at $90 ^ { \circ }$ to the first sheet. What is the intensity of the light emerging from the fourth sheet in terms of $I _ { 0 }$ ?