The value of x is -6, and the value of y is -34. You can figure this out by setting the two equations equal to each other, so it would look like: 5x-4 = 7x+8. Then, use the addition property of equality by adding 4 to both sides of the equation to leave x by itself. After, use the subtraction property of equality by subtracting 7x on both sides to get x by itself. Finally, use the division property of equality by dividing both sides of the equation by 2, to get x by itself. This will give you the value of x or -6. To get the y value, simply substitute x into the original equations.
Hope this helps ^-^