If KN = 9 cm, MN = 21 cm, RS = 42 cm, and PS = 18 cm, what is the scale factor of figure PQRS to figure KLMN?

If KN = 9 cm, MN = 21 cm, RS = 42 cm, and PS = 18 cm, what is the scale factor of figure PQRS to figure KLMN?