x = 0 or x = -1
You can solve this by using the second equation, which is already solved for y and subbing that in for y in the first equation.
14x + (3x^2 - 11x - 4) = -4
14x + 3x^2 - 11x = 0
3x^2 + 3x = 0
Then you can solve by pulling out the greatest common factor
3x(x + 1) = 0
Then set each part equal to 0
3x = 0
x = 0
x + 1 = 0
x = -1