First, you are not putting the expression correctly. I'm assuming you are mean to say (ab)². This is because if you want to multiply by 2, the 2 usually goes first like this 2ab. But it's not case, so, it should be as I said.
Now, let's replace the values for a and b into the expression:
Since there are five short-answer questions and she randomly selects one for a quiz, this can be written as 1/5 because there are 5 choices, but only one can be selected.
Therefore, the probability that she will select question #3 is a 1/5 or 0.2 chance.