Consider the following premises. For all x_6, x_6 will work. For all x_6, x_6 will write a letter or x_6 will not work. For all x_6, x_6 is happy. Can we infer the following from them? If we can, name the inference rule being used: For all x_6, x_6 is happy.
That is one of the premises. Therefore, the answer is yes.