The 12-12 should cancel itself, the rest of the equation you bring down to get
2x=12 (because 24-12=12)
Now you have 2x=12. you then divide 2x by both sides.
2x=12
/2x=/2x
The 2x/2x cancels itself out so you then solve for 12/2x.
For this you just divide 12/2 which is 6!
x= 6 is your final answer. to check this equation you can plug your number back into x to see if it is true! 2(6)+12=24. 6 times 2 is 12 and 12+12 is 24 so your answer (6) is true!