What is the inverse (opposite) of addition?

You were told that the amount of time lapsed between consecutive trades on the new york stock exchange followed a normal distribution with a mean of 15 seconds. you were also told that the probability that the time lapsed between two consecutive trades to fall between 16 to 17 seconds was 13%. the probability that the time lapsed between two consecutive trades would fall below 13 seconds was 7%. what is the probability that the time lapsed between two consecutive trades will be between 14 and 15 seconds?

Icould really use some with this question.

Evan walked 5/8 mile to his friends house.then together they walked 7/12 mile to the movie theatre.which pair of fraction can evan use to find how far he walked in all?