Consider the following premises. For all x_6, if x_6 were fast, then x_6 is drinking water. There is at least one x_6 for which x_6 is happy. For all x_6, x_6 is happy if and only if x_6 will drink water. Can we infer the following from them? There is at least one x_6 for which x_6 will drink water.
 From the fact that for all x_6, x_6 is happy if and only if x_6 will drink water we can infer that for all x_6, if x_6 were happy, then x_6 is drinking water. From the fact that there is at least one x_6 for which x_6 is happy we can infer that there is at least one x_6 for which x_6 is happy or x_6 is fast. Finally, from the fact that for all x_6, if x_6 were happy, then x_6 is drinking water, that for all x_6, if x_6 were fast, then x_6 is drinking water, and that there is at least one x_6 for which x_6 is happy or x_6 is fast we can infer that there is at least one x_6 for which x_6 will drink water. Therefore, the answer is yes.