You gave no options but the simplest way to solve this is to set it equal to all of the answers to see if it is correct.
Answer:
20
Step-by-step explanation:
4/16 = 2/8 = 1/4= 0.25
You started of with 84
13
Pythagreom Therom:
a^2+b^2=c^2
12^2+5^2=c^2
144+25=c^2
169=c^2
c=13