The answer is C.
To solve, add 2x to both sides. Then subtract 11 from both sides. Finally, divide both sides by 4 to get x = -7.5. This is the only equation that has exactly one solution. For answer choices B and D, there are an infinite number of x values so, these two can easily be ruled out. And for answer choice A, there is no solution because the x values cancel each other out.
2x + 11 = -2x - 18
4x + 11 = - 18
4x = -29
x = -7.5
Hope this helps! :)
