Consider the following premises. There is at least one x_3 for which x_3 is sad or x_3 will not take a plane. For all x_3, if x_3 were sad, then x_3 is a cashier. Can we infer the following from them? There is at least one x_3 for which if x_3 takes a plane, then x_3 is a cashier.
 From the fact that there is at least one x_3 for which x_3 is sad or x_3 will not take a plane we can infer that there is at least one x_3 for which if x_3 takes a plane, then x_3 is sad. Finally, from the fact that there is at least one x_3 for which if x_3 takes a plane, then x_3 is sad, and that for all x_3, if x_3 were sad, then x_3 is a cashier we can infer that there is at least one x_3 for which if x_3 takes a plane, then x_3 is a cashier. Therefore, the answer is yes.