Answer: The required scale factor of ΔABC to ΔRST is 
Step-by-step explanation: Given that triangles ABC and RST are similar, where
AB = 18, BC = 15, AC = 9 and RS = 6.
We are use a proportion with sides AB and RS to find the scale factor of triangle ABC to triangle RST.
We know that the scale factor of dilation is given by

Since AB and RS are corresponding sides of the two similar triangle ABC and RST, so the scale factor of ABC to RST is

Thus, the required scale factor of ΔABC to ΔRST is 