Just to follow up on the math below, I guess the only conclusion I can offer is the following, hoping it can help writers, if nothing else, understand just why it is so difficult to break into, or sustain, standard traditional model publishing via an agent:

With the best will in the world, the best agent in the world seeing an average first time novelist's baby hit their desk can only afford to spend 8 hours or so packaging, shopping, and closing the sale on that first novel. That is, unless you are destined for glory, in order to break into the business via this route your first novel has to be readable and sellable by your prospective agent in a single day's work.

And for the working pros, not the biggest of the big but the reliable sellers who can hit that 40K advance book after book, the best agent in the world can afford a week for each book, instead of a day. So, assuming that level of agent and writer and editor are a good working team, sell on emails and clean manuscripts, basically I'd estimate that that week's time is devoted to your basic promo, booking tours, etc.

Again, averages, all things cannot ever be equal in this sort of thing, your mileage may vary, no warrantees admitted to or implied, buckle your seatbelts, etc.