Please stop attaching word documents and start typing the questions out.

I assume you know how to get the prior probability (the sample of 50 is assumed to come from a large population so that the Binomial distribution can be used etc.).

For convenience, let A be the event 3 items in the sample are non-defective. is the prior probability and is the posterior probability. Then:

is already got.

Now substitute , and into and simplify.