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Use addition or substitution to find the value of x for this set of equations.top line 4x + 13y = 40 bottom line 4x + 3y = -40

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2 Answers

   4x + 3y = -40
 —  
   4x + 13y = 40   
   0   -10y  = -80 ----> y = 8
Let's substitute "y" by 8 in first equation
   4x + 3*8 = -40 ----> 4x + 24 = -40 ----> 4x = -40 - 24
                                                               4x = -64
                                                                 x = -16
      The answer is (-16, 8) 

Comments

4x+13y= 40

4x+3y= -40

___________

subtract equation 2 from equation 1:

4x+13y =40

-4x-3y   =-(-40)

______________

10y = 40+40=80

y=8

substitute y=8 in equation 1 or 2

4x+ 3y= - 40

4x + 3 (8) = -40

4x + 24= -40

4x= - 40-24

4x= -64

x = - 16