This is a valid argument based on “most” and “all.” In addition, the conclusion is weaker than what could have been concluded.

Premises:

dinners at Cafe Delice -most→ main kitchen
main kitchen → teacher at Culinary Institute

Conclusion:

dinners at Cafe Delice -some- teacher at Culinary Institute

The two premises do not involve the combination of “most” and “all.” (They involve two “all” statements.)

This is an invalid argument, so it can’t parallel the valid argument in the stimulus. We can’t conclude that some dinners are prepared by Culinary Institute teachers, because even though those teachers are “allowed” to use the main kitchen, that leaves open the possibility that other people are also allowed to use the kitchen. Those other people could prepare all dinners at Cafe Delice.

This is an invalid argument, so it can’t parallel the valid argument in the stimulus. We can’t conclude that some dinners are prepared by Culinary Institute teachers, because even though most of those teachers are “allowed” to use the main kitchen, that leaves open the possibility that other people are also allowed to use the kitchen. Those other people could prepare all dinners at Cafe Delice.

This is an invalid argument, so it can’t parallel the valid argument in the stimulus. We can’t conclude that some dinners are prepared in the main kitchen, because even though dinners are usually prepared by Culinary Institute teachers, those teachers might use a different kitchen to make those dinners. We know the teachers are the only ones allowed to use the main kitchen, but they could have access to other kitchens and prepare the dinners at those other kitchens.