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