Associative property I think.
2. (2.25 • 23) • 4
2.25x23=51.75
4x51.75=207
right
Although we're not really using the associative property. That would state that
(2.25 • 23) • 4 = 2.25 • (23 • 4)
All you did was evaluate the expression inside the parentheses and replace it with an equal value.