"Usually" is a bit too general (you may be thinking of Cheby when dealing with a standard normal). In any case all you're asked to do is verify that the probability that any r.v. falls outside your specified limits (on the left or the right) is simply 1/4 in total. This amounts to integrating from -1 to -7/9 and, 7/9 to 1, and summing the result (I'll leave the whys to you).