Here the 99 comes from the product of the other two modulii, 9 and 11 in the system. The solution here is applying the general formula described in 7.6.

The first term of this general equation, is 2 (from the first equation in the system) times 4 (which is the mod. multiplicative of 9*11) times 9*11 (from the other two modulii).

Note: This general equation can be a little confusing, and probably isn't the easiest way to actually solving questions like this involving the Chinese Remainder Theorem. It is okay to just know that by the Chinese Remainder Theorem we are guaranteed a solution, and then you can try to solve the equation directly, like explained in Solution 2 there.

Hence, a method similar to Solution 2 in the textbook is probably how I'd recommend solving this system.