We can eliminate 0.6, since that would result in a smaller shape, not a larger.
If the scale factor was 2, then each coordinate for every point on the original shape would be multiplied by 2.
For example, (3,3) would become (6,6), but it didn't. So that rules out the scale factor of 2.
If the scale factor was 1.5, then each coordinate for every point on the original shape would be multiplied by 1.5.
For example, (3,3) would become (4.5,4,5), and that checks out.
Then (4,4) would become (6,6), and that also checks.
And (5,3) would become (7.5, 4.5), and that looks right.
Finally, (2,5) would become (3, 7.5) and that also look good.
I'd say the scale factor is 1.5.