-8x-12+5x=-39
Collect like terms equations

x = 9

Step-by-step explanation:

-8x - 12 + 5x = -39     Collect or combine like terms on the left side by add -8x and 5x.

(-8x +5x ) - 12 = -39  

-3x - 12   =  -39         NOw add 12  to both sides

     + 12       + 12

-3x  =  -27     Divide  both sides by -3

x = 9

x=9.5 and y=5.5

Step-by-step explanation:

x+y=15

x-y=4

add

2x=19

x=9.5

y=15-9.5

y=5.5

x=9.5 and y=5.5