Answer:
B. 4
Step-by-step explanation:
The given function is of the form:

A is called the amplitude of the given function.
We can read from the graph that, the function ranges between:
-4 and 4
This implies that:

Therefore the amplitude of the function is 4.
Hence the value of A must be 4.
Theoretical probablity=desiredoutcomes/totalpossibleoutcomes
desired=number of white marbles=20
total possible=red+blue+white=30+50+20=100
so theoretical probablity=20/100=2/10=0.2=20%