Just getting started - and stuck already :)

Hi everybody,

I am just getting started with PowerBI, and stuck already :). Here is my question:

I have 2 tables. 

Table A holds unique IDs: 

1

2

3

4

Table B holds the same IDs and Country Names:

1 Belgium

2 Belgium 

2 France

2 China

3 France

4 France

4 Belgium

What I would like to do is add a column to Table A providing a sum of the number of distinct countries in which the ID is available. In other words, Table A should become:

1 1

2 3

3 2

4 1

Any ideas on how I can best achieve this?

Thanks so much!
Mark