How did you determine whether the test to be used is one tailed or two tailed?
A one-tailed test has the entire 5% of the alpha level in one tail (in either the left, or the right tail). A two-tailed test splits your alpha level in half (as in the image to the left). Lets say yore working with the standard alpha level of 0.5 (5%). A two tailed test will have half of this (2.5%) in each tail.