Answer:

Explanation:
P(not C) is the probability of C not being selected, which in this question, is equivalent to 0.15 + 0.2 + p + q (i.e. the sections not in bubble C).
Hence,
0.83 = 0.15 + 0.2 + p + q.
0.83 = 0.35 + p + q
0.48 = p + q
Thus, this is the first equation in our system:

The next equation in our system comes from the fact that P(B) = 2P(A).
P(B) = p + q + 0.05
P(A) = p + 0.15
Thus, 2(p + 0.15) = p + q + 0.05
Distribute "2"
2p + 0.3 = p + q + 0.05
Group like terms
q - p = 0.25
Thus, this is the second equation in our system, and allows us to solve via elimination.

Adding the 2 equations yields:

Thus, q = 0.365.
Thus, p = 0.115
Now, because everything in the diagram must sum to 1.00, plug in every value to get:

Simplifying, we get:
0.88 + r = 1
Thus, r = 0.12.
Hope that helped and let me know if you want me to elaborate on anything :)