Consider the following premises. There is at least one x_4 for which if x_4 were a bartender, then x_4 is happy. For all x_4, x_4 is sad. For all x_4, x_4 is a bartender. Can we infer the following from them? If we can, name the inference rule being used: For all x_4, x_4 is not sad.
That contradicts the premises. Therefore the answer is no.