What property is this (3 5) 4=3 (5 4)?

Hey there! Hello!

It's a bit hard to answer your question without knowing exactly what signs you're using, but I assume that this has to do with either multiplication or addition. Feel free to comment and correct me if this isn't the case, and I'll help you out further. 

If all of the signs are meant to be multiplication signs, this can be represented by the Associative Property of Multiplication. If the signs are meant to be addition signs, this can be represented by the Associative Property of Addition. This property basically states that the result of adding/multiplying these numbers together will always be the same no matter which order they are in. 

You could test this out by actually adding/multiplying these numbers together. This gives you 12 = 12, or 60 = 60, respectively. 

Hope this helps you out! Again, feel free to ask any additional questions if you need further clarification. :-)