You would solve for x. Example- 5-x=12, you would do the opposite sign of the number with the variable on the same side, which is 5. 5 is positive so you would subtract 5 from both sides. So subtract 5 from 5 and subtract 5 from 12. Then you would be left with -x=7. Finally, you would divide -1 from both sides. Concluding with x=-7