You have created a custom module which must perform an action immediately after an order is placed, but only on the store front of the merchant site. You have selected the checkout_submit_all_after as the target event which the module will observe.
In which file will the event observer be declared?

You are developing a new theme which inherits from the Magento_Luma theme.
How is this accomplished?

Which layout file should be used for a product with a specific id?

You have created a new block and will be adding this block on every page. The block contains user-specific information and cannot be cached. The block is added to the default.xml with:

What does this accomplish?

A merchant sells shoes with multiple variations such as a color and size. A shoe is represented by a configurable product. There are seven different colors and four sizes.
What is the minimal amount of simple products that represent a combination of color and size needs to be created in order to make a shoe salable?