Comparing 2 identical destructive tests

#1
1 lot of production contains 558,000 units
Units are randomly chosen for test at 2 different locations.
Tested first at location A, then lot is shipped to location B, goes through some process and tested again.
Assume the 2 tests are identical in all aspects.
The test is destructive in nature so same part cannot be tested twice.
At location A, 7200 units are tested, 0 failures are recorded.
At location B after the additional process, 4400 units are tested, 6 failures are recorded.
What is the probability that the fails were present in the lot and were not caught at location A?
What is the probability that the failures were caused by the additional process at location B?
Appreciate your responses, please let me know if any additional information is required.