With the associative property, it does not matter which order you multiply numbers in. The answer to 4*5 is the same answer as 5*4. This works with more than two numbers as well. The associative property of addition also works this way.
In this question, it is important to watch where the parentheses are placed.
ANSWER: C) 4(2a * 5) = (2a * 5) * 4. Multiplying 4 to the left or the right of the set of parentheses will result in the same answer.
Hope this helps! :)