To find the length of side WX, we first need to find the length of side ST in figure WXYZ.
Using the scale factor of 3:1, we can set up a proportion:
117 mm (ST) / 3 = x / 1
Solving for x, we get x = 117 mm / 3 = 39 mm
Now, since STUV and WXYZ are similar figures, the ratio of their sides is the same. Therefore, the length of side WX is 39 mm * 3 = 117 mm.
Therefore, the length of side WX is 117 mm.
Answer: A. 459 mm