In 2015, a company made 2.7×10^11 mailboxes. in 2019, the same company made 3.9×10^12 mailboxes. how many more mailboxes did they make in 2019? (write your answer in scientific notation.)

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