The ratio of side lengths is approximately 1.4.
We need to first figure out which sides correspond to which.
13/9.29 = 1.39935 which is close to 1.4, so the sides 13 cm and 9.29 cm are corresponding sides.
8/5.71 = 1.401 which is close to 1.4, so the sides 8 cm and 5.71 cm are corresponding sides.
That leaves the 7 cm side corresponding to the unknown side.
7 cm/1.4 = 5 cm
Answer: D. 5 cm
