Answer:
2x+13=1, Given.
2x+1=3, multiplied both sides by 3.
2x=2, subtracted 1 from both sides.
x=1, divided both sides by 2.
NOTE: Your school may use special names for all of those proofs. If so, I don't know what they are. Sorry.
Explanation:
For the first non-given statement, everything is over 3. A simple law of fractions is that the top number/s is being divided by the bottom, so all we need to do to reverse it is multiply it all by 3. This includes the other side.
For the second, it begins to get much easier as we've past the hardest step. Subtracting 1 from both sides gets us 2x = 2.
For the third, it is again easier. All that's left is to divide by 2 because that's what x is being multiplied by. After we do that, x turns out to be 1.