Which statement about this argument is true?

argument:

if today is saturday, then there is no school.

today is saturday.

there is no school.

the argument is valid by the law of syllogism.

the argument is valid, but does not follow the law of syllogism or the law of detachment.

the argument is valid by the law of detachment.

the argument is invalid.

The management of a supermarket wants to adopt a new promotional policy of giving a free gift to every customer who spends more than a certain amount per visit at this supermarket. the expectation of the management is that after this promotional policy is advertised, the expenditures for all customers at this supermarket will be normally distributed with a mean of $95 and a standard deviation of $20. if the management wants to give free gifts to at most 10% of the customers, what should the amount be above which a customer would receive a free gift?