If 8 becomes 6, what is its percent of decrease?

Can someone me with this problem . show your work .

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

If f(x) = 2x + 8 and g(x) = x4, what is (gº)?