[High School - Geometry] Two-Column Proofs

[Crashfan3]

First post here. Checked the rules, hoping it isn't breaking any.

My teacher has tried twice to explain this to me, but I just can't get it into my head.

Here's my review problem. Now, keep in mind that I can go look up the answer. This is only to help me practice for Friday's test.

Given: QR = x + 3
Given: RS = 2x
Given: QS = 42

Step 1: QR + RS = QS
Step 2: x + 3 + 2x = 42
Step 3: 3x + 3 = 42
Step 4: 3x = 39
Step 5: x = 13


There's the problem, fully solved, with all work shown. What I need to do is justify each step, by saying which property and/or process they are using with each step.
I need someone who's good at this to help me understand where these properties and processes are being used.

Thanks.

[emerald000]

I am assuming that Q,R and S are dots and aligned on a line.

1- The line between two dots can be cutted in as many pieces you like and their sum of their length equals the length of the initial line.

2- That must be the lenght of the given line segments. (If QR=x+3 and RS=2x, then QS=x+3+2x)

3,4,5- Simple algebra.

I hope this is clear and that the context I took is right. If you have questions, just ask.

[Crashfan3]

emerald000: That should be helpful, I'll just match that with all the complicated names they want me to write down in place of the logic (e.g. Step 1 would be Transitive Property of Congruence [if a=b, and b=c, then a=c]). Now I'll just need to try and memorize those before the test. I wish we could use notes on the test... :/