If we draw both triangles, we get the following:
notice that the transformation on triangle 1 made it smaller, then, we have a dilation.
To find the scale factor, we have to remember the general rule for the dilations on the cartesian plane:

in this case, we can take the point A' on triangle 2 and the point A on triangle 1 , assuming that the transformation gave us the point on triangle 2:

solving for k, we get:

therefore, the scale factor is k = 1/3