To find an equation that doesn’t have a solution, we must show that said equation can represent something that isn’t true, so lets go through each option and determine if it has a solution or not. For choice A, we can combine the right side into 6x and we get 6x = 3x, which we can turn into 3x = 0. This does have a solution (x = 0), so A is not correct. We can do the same thing for choice B; we get 6x + 1 = 4x, which turns into -2x = 1, so x = -1/2, meaning choice B has a solution. When we do the same thing to choice C, we get x = -2, meaning it has a solution. When we look at choice D, we get 6x + 3 = 6x, and if we subtract 6x from both sides we get 3 = 0, which is not true, meaning this equation does not have a solution. D is the correct answer.