Sara has two boxes. There are 6 black and 4 white in Box A. There are 7 black and 3 white counters in Box B.
Sara takes at random a counter from box A and puts it in Box B.
She then takes at random a counter from box B and puts it in Box A.

Using a probability tree diagram, find the probability that after Sara has put the counters from Box B into Box A there will still be 6 black counters and 4 white counters in Box A.

(Note: Please just don't give the answer straight to me, please include explaining and step by step guide to how to get the answer.)

Thank You

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