In this problem, we are asked for the volume of the pool filled with water. In this case, the volume of the rectangular prism is equal to length times width times height. Since length and width are equal, the formula includes the squaring of the length. after substitution, the formula is 9^2 * 5 equal to 405 m3.
Complementary events are those events that are opposites of each other. i.e. in this case the complementary event for choosing a green marble is not choosing a green. It has nothing to do with choosing or not choosing marbles of colors other than green.
