If you are not interested in an exact answer, or if you would like to verify that your answer is in the ballpark, just notice that z=1.96 means that you are ALMOST 2 standard deviations above the mean. (It's 1.96 standard deviations - but we are talking a rough estimate.) Two standard deviations is 2 * 15 = 30. So take the mean and add 100 + 30 = 130. This is not an exact amount, but you can see that it is close to the answer that Varaia gave you of 129.4.
