Answer
Valid. The major and minor premises are diagrammed. There is only one way to compose both premises.
Work Step by Step
The major premise says the set of people is included in the set of mice. The minor premise says the set of mice is included in the set of mortals. Assuming both of these premises are true, it must follow that the set of people is included in the set of mortals. Since it is impossible for the conclusion to be false if the premises are true, the argument is valid.
