Using the associative property of multiplication, which expression is equivalent to 5(9x)?

a.5(9 + x)

b.9(5x)

c.45x

d. (5x9)x

D (5x9)x because the parentheses are switched but the values are the same

The associative property states that you can move parenthesis around without affecting the solution to the equation/expression.
Example:
5 • (3 • 2) = (5 • 3) • 2
Which is also written as 5(3•2) = (5•3)2

A is not correct either way since adding and multiplying would have completely different results.
B moves the values, not the parenthesis, although it would be the same.
C uses the distributive property, not associative.
D uses the associative property and is correct.
So the answer is D.