Ah, the commutative property.
a + b = b + a
xy = yx
When using the commutative property - a good way to remember it is to think of a community, in which each community member helps one another to a mutual outcome.
Using the commutative property we can rearrange this equation into a more sensical format:
-8.9 + 6.7 - 1.1
6.7 - 1.1 - 8.9
6.7 - 1.1 = 5.6
5.6 - 8.9 = -3.3