Solve for first two positive solutions sin(3x)cos (4x)+cos(3x)sin(4x)=-0.9

A. 90 degrees b. 45 degrees c. 30 degrees d. 120 degrees

How to do this , and can some one explain

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