The amount of exposure to radiation that a person receives is not affected by

A. Total time of exposure
B. Distance from the source
C. Degree of radioactivity of the material
D. Size or weight of the radioactive source
E. None of the above

a, b, c - sides of a triangle

a + b > c

a + c > b

b + c > a

we have a = 5m and b = 11m. substitute:

5 + 11 > c

16 > c → c < 16

5 + c > 11         subtract 5 from both sides

c > 6

11 + c > 5         subtract 11 from both sides

c > -6

c < 16 and c > 6 and c > -6

thereofre your answer is 6m < c < 16m

yes. i think it is for sure.