The 6,000 oranges harvested at an orange grove are a combination of Valencia and Navel Oranges. The ratio of Valencia Oranges to Navel Oranges is 7 : 5. The owner of the orange grove finds that 1 in every 20 valencia oranges and 1 in every 25 navel oranges are rotten

a) What fraction of oranges are not rotten?

b) What is the probability that a randomly selected orange is a good orange?

c) What is the probability that a randomly selected orange is a rotten Valencia?