Since these are parallel lines they are equal to each other. You need to combine the like terms and have the -7 by itself.
1. Subtract the X and move it to the other side so your equation looks like : 2x-x-7=0.
2. Next move the -7 to the other side ; 2x-x=7
3. Finally combine like terms; 1x=7
Final answer should be x=7 after dividing . Hope this helps!