What method would be the easiest to solve this equation?

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

Use the elimination method to solve the systems of equations. choose the correct ordered pair. 7x+4y=39

The surface area of the triangular prism is .