Respuesta :

4. 6x + 5y = 4  a
    6x-7y = -20  b

a-b  
6x + 5y -6x+ 7y = 4+20
12y = 24 
y = 2

Sub y in a 
6x + 10 = 4
6x = 4-10
x = -6/6 = -1

5. 2x-3y=12  a
    4x+ 3y = 24   b

b+a

4x+3y+2x-3y =36
6x=36
x=6

Sub x in a 
12-3y = 12
-3y=12-12
y= 0/3 = 0