How do i find the mean absolute deviation of a data set

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling

I'm confused on this could anyone me and show me what i need to do to solve it.

Angles r and s are complementary. the measure of angle r is 31 degrees. which equation can be used to find angle s?