Answer: 2
Explanation:
Given : The image of polygon MNOP after a similarity transformation is polygon WXYZ each side of MNOP is two times as long as the corresponding side of WXYZ .
i.e. 
 [ Since MN corresponds WX ]
We know that for any two similar geometric figures, the scale factor is the ratio of their corresponding sides .
i.e. 

Hence, the the scale factor of the dilation in the similarity transformation =2