16 = -4(r+2)

First multiply everything in parenthesis by -4

16 = -4r -8

Next, add 8 to both sides.

24 = -4r

Now we divide both sides by -4. (Remember, positive divided by negative is a negative).

-6 = r

27 = -9(z-1)

Multiply everything in parenthesis by -9.

27 = -9z + 9

Subtract 9 from both sides.

18 = -9z

Divide both sides by -9.

-2 = z

16 = -4(r+2)

16= -4r-8

16+8 = -4r

24 = -4r

4r = -24

r = -6

27 = -9(z-1)

27 = -9z + 9

27-9 = -9z

18 = -9z

9z = -18

z = -2

just do the opposite to bring to other side. (* =multiply opposite is divide /)

16 / -4 = r+2

-4 = r+2

-4 – 2 = r

r = -6

then going backwards

16=-4(-6+2)

16 = -4 * -4

16 = 16

is correct and true.