I think that is a good question. It's not an easy mathematical problem that can be solved on the DAT. However, I think the faster way may not be solving the problem with raw power, instead go through the answer choices and pick the one that match.
One way I go about doing this is convert it to x^2=13 * 10^-10. Then we can solve the squart root of 10^-10, and the squart root of 13 is somewhere between 3 and 4.
Keep in mind that the Topscore general chem questions usually requires more raw calculation than the actual test itself. Best wishes.
