Consider the following premises. Karen is not fast. If Barbara were happy, then Karen is fast. Robert is drinking water or Barbara is happy. Can we infer the following from them? Robert is drinking water.
 From the fact that if Barbara were happy, then Karen is fast, and that Karen is not fast we can infer that Barbara is not happy. From the fact that Robert is drinking water or Barbara is happy we can infer that if Barbara were not happy, then Robert is drinking water. Finally, from the fact that if Barbara were not happy, then Robert is drinking water, and that Barbara is not happy we can infer that Robert is drinking water. Therefore, the answer is yes.