Combining like terms is pretty simple. First, you would identify which terms are similar to what terms. For example, you can't combine two terms that aren't similar like 2x and 3y. It would have to be 2x and 3x to combine. Next, be sure to add/multiply/subtract/divide/etc. the terms. For example, if you had the problem 2x + 4x + 3y, you would combine the "x" terms and the resultant problem would be 6x + 3y. Hope this helped :)
Guessing you meant by a factor of 3... not 13 since none of the solutions are anywhere close to that.
to compress is to smoosh.
It's the equation of a line. If you smoosh it vertically the line becomes flatter and the slope smaller.
Essentially g(x) = 3f(x)
3y = 12x + 6
y = (12/3)x + 6/3
y = 4x + 2