I encountered a similar problem but it had choices. These were its choices:
     A)	1 : 3	
            B)	1 : 1	
            C)	3 : 1	
            D)	3 : 3
Dilation with a scale factor of 3 means that the original triangle was made bigger and created the resulting triangle. 
PQR was the original triangle. XYZ was the resulting image and it is 3 times the size PQR. Thus, the ratio of the perimeter of triangle PQR to the perimeter of triangle XYZ is 1:3