Matching number in complete bipartitite graph

Question

I am not convinced by this. Please explain or please tell me the source from where I can clear this out.

Comments

The first vertex in V1 (having 4 vertices ) will have 6 choices , then 2nd will have 5 

3rd will have 4 and last vertex wil have 3 choices that gives   6*5*4*3= 360 . . please explain ,im really confused now.

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For more: matching number of $K_{m,n}$

Answer 1

Matching number is #f non Adjacent edges.

Take K3,2

Here, matching no is "2" which is min {3,2}

Comments

Now I get it.  They are asking for matching no.

I thought how many matchings can be present. .