If an image of a triangle is congruent to the pre-image, what is the scale factor of the dilation?

what am i looking for finish the question.

step-by-step explanation:

1) the property is   ixi = a ⇔x = a   o x = -a

4(x-5)+3= 15⇒4x-20+3 = 15⇒4x-17= 15⇒4x = 15+17⇒4x = 32⇒x =32/4= 8

4(x-5) +3= -15⇒4x-20 +3 = -15⇒4x-17= -15⇒4x =-15+17⇒4x = 2⇒x =2/4= 1/2

the values are x =8 and x = 0,5

is it like a multiple choice? if so then i need the multiple choice so i can get and understanding on what the answers is so that i can explain it to you