PLEASE HELP ME ASAP FOR 11 and 15 show all your work FOR 30 points and BRAINLIEST

Answer:
11. (-3, -1)
Step-by-step explanation:
11.
-8x+y=23
solve for y by y= 23+8x
substitute the given value of y into the equation
-x-4(23+8x) = 7
solve for x and get x = -3
substitute the -3 for x
y= 23+8 x (-3)
y= 23 + (-4)
y = -1