Answer
A. 60%
Explanation
If a candy is blue, you are already restricted to 50 candy (20+30) which are blue, exclude the other candy which are red or white.
From there you have to find the probability that the blue candy contains no nuts.
The formula needed:
No. of Blue candy that contains no nuts / total blue candy
That would be
30/50 = 60%
<~>\_/<~> Ho_odini <~>\_/<~>