AS per given by the question,
There are given that 9 red marbles, 7 blue marbles, 5 yellow marbles and 3 white marbles.
Now,
The total numbers of marbles in a bag is;

Then,
The probability of getting white marble is;

So,

Now,
According to the question,
The probability that the marble is not white,
Then,

So,

Hence, the probability that getting not white marbles is 0.875.