Is each pair equivalent or not ?

1 and 3 are true.

Step-by-step explanation:

For the first equation, you would add 2x to each side to result in the second equation.

For the third equation, you would divide by x on both sides, resulting in the second equation.

2. is not correct because the 3 is gone, and was "divided" from (x-4), but not the 15.

4. is not correct because of the extra x that is included in the second equation. That x makes the equations False.