Write .0045 into a 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

Solve this problem! extra ! 3025/5.5 = a/90.75

What is the approximate value of  x  in the equation below.–3.396–0.7080.3040.955