SQL Server Update statement

I'm unsure how to write an update sql server that appends additional value.  I have a table A and table B.  There is column called Text in Table B that needs additional info appended at the end If the table A Event column has value of 20.    

Here is what the tables look like:
 
 
What I want to do is keep the existing text value (in table B column Text)  and add  the verbage "plus cat" if the Table A Event  column has value of 20.  For example add "plus cat" to Text column to say "mouse2 plus cat"  for all Table A records that have Event code 20.  When I join the tables, this is what my results should look like:


 

thanks
np