What is this property: 7+(4+4)=(7+4)+4

When i add money am i supposed to make it like this 7+12 or 7.00+12.00 because i got 19 dollars for my answer

How do you use the elimination method for this question? explain, because i really want to understand!

White shapes and black shapes are used in a game. some of the shapes are circles. while the rest are squares. the ratio of the number of white shapes to the number of black shapes is 5: 11. the ratio of the number of white cicrles to the number of white squares is 3: 7. the ratio of the number of black circles to the number of black squres is 3: 8. work out what fraction of all the shapes are circles.