Which property is shown (5×3)+(5×9)=5×(3+9)

Resolve to do so
5x3=15 
5x9=45 
3+9=12
15+45=5x12 
15+45=60 
5x12=60 
60=60
Which property is shown I did not understand but I think with the result 60 = 60 alone, but you will understand if you can not send me a comment, so I'll try to make you understand  =)