I'm having a hard time with this fog problem

I don't get what the subscipt to the upper left of the square root sign is supposed to mean, which means I have no idea how to do the problem. 10 points to the willing.

http://i53.tinypic.com/2d8kf35.gif

the superscript 3 means "cube root" not square root
do you understand the rest of the equation?