5-2.1=? 5-2.17=? 5-2 7/8 solve make sure to re-check your self before answering or no forty points

Can someone explain the elimination method to me for this problem?

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

What is the value of the product (3-2i)(3+2i)?