-3x + 7 y = -16
-9x + 5y = 16

Step-by-step explanation:

-3x + 7y = -16   (-3)  to eliminate x

-9x + 5y = 16

9x - 21y = 48

      -16y = 64

           y = 64/-16

           y = -4

substitute y= -4 into eq. 1

-3x + 7y = -16

-3x + 7(-4) = -16

-3x = -16 + 28

  x = 12 / -3

  x = -4

check:

-3(-4) + 7(-4) = -16

- 16 = -16 ok

-9x + 5y = 16

-9(-4) + 5(-4) = 16

16 = 16  ok

x=44/3, y=4

Step-by-step explanation:

Assuming you have to solve for x and y

-3x+ 7y = -16 (1)

-9x+ 5y =16 (2)

multiply (1) by -3 and add it to (2)

9x-21y=48

-9x+5y=16

Add up and get

-21y+5y=48+16 combine like terms

16y=64 divide both sides by 16 and get

y=4

Substitute y=4 in (1)

-3*x+7*4=-16

28+16=3x

44=3x

x=44/3

it would open into a square depending on the type of envelope i’m not sure about the second part