Solve this multi-step equation 6-x-x=18

Regular price is $77.00 and the discount is 5% find the sale price

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

The radius of the earth is two times the radius of the moon. what fraction of the volume of the earth is the volume of the moon?