I need help on this one, please!

Answer:
Option B,14.6 cm and D,20.3 cm
Step-by-step explanation:
Let a and b represent the lengths of the two known sides such that a≥b. Let c represent the length of the unknown side, the length of c must fall within
a−b<c<a+b
11.9-9.1<c<11.9+9.1
2.8<21
By elimination,
Option B and D remain, i.e 14.6 cm & 20.3 cm