The problem is actually already factored for you. They are asking you to just set the equation to zero. Find the zeros.
The most likely answer is vary greatly all year long. This is so, because of the different parts of the ocean, sometimes with higher temperatures, near the Florida keys, or in some waters in the gulf of Mexico, and colder waters, such as antarctic waters. Because of the weather changes, some parts of the ocean may freeze over, while some other parts are still free-flowing.
First, you need to choose a yellow marble. That is 6/15.
Next, you need to choose a blue marble. That is 5/14, because 1 yellow marble would have been "chosen" already.
So the probability altogether is 6/15 * 5/14 = 1/7, or about 14%.
