Which answer choice shows that the set of irrational numbers is not closed under addition?

pi + -pi = 0

Step-by-step explanation:

We need to have irrational numbers that we are adding and end up with a rational number.  This means that it is not closed under addition

pi is an irrational number

0 is a rational number

pi + -pi = 0

irrational + irrational = rational

x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18

13.46

step-by-step explanation:

16.80 x .20 = 13.46