First I would distribute the left part like so:
12x - 18 - (5x + 7)
Then I would distribute the right side like so: (I'm just distributing a negative sign)
12x - 18 - 5x - 7
Then I combine like terms like so: (12x and -5x)
7x - 18 - 7
Then I would combine the other like terms like so: (-18 and -7)
7x - 25
I hope that helps! Feel free to let me know if you have any questions! :3
- mathwizzard3