With this being said, any value greater than 17 will be a solution. In the choices given, only 19, 21, and 36 are greater so those are the possible solutions. The others are not solutions.
So first we would plug in the first term which is 2 so we would get times so next we would see that the common ration is -3 since every time the number is being multiplied by -3. so then our equation would be times . Now we would just find the choice that matches and it would be the second choice.