What math property is 3+(-6)=-6+3

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

Vinay constructed this spinner based on the population of teachers at his school according to vinays model what is the probability that he will have a male history teacher two years in a row

If private savings 'v' = 0.75s and total savings 's' equals $4.20 billion, solve for public and private savings.