Which expression is equivalent to (3x + 6) + 4x?

A. 3x + 10

B. 7x + 6

C. 12x + 6

D. 13x

Can someone be awesome and me with : (

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

Landon wrote that 3−2.6=4. which statement about his answer is true?