With that out of the way, I'm going to throw some caveats at you. The idea is not to discourage you, just to make sure you realize the effort that will go into preparing for those 40 hour of training you will deliver and price yourself accordingly.
As a first timer on professional training, be aware that 20+ people to train is a large number. You won't be able to achieve much personal interaction with each student, and you might find a great deal of variance in their backgrounds and skill levels at the start of the course. Be prepared for outliers, at both ends of the spectrum, they can chew through time that would be better spent on topics for the bulk of the class.
You will also find that large firms can be notoriously bad at gauging the needs of their teams, you could deliver exactly what is asked of you by the management without meeting the dev team's needs. Take a moment at the start to gauge the team's expectations, explicitly ask them what they want to get out of the training and try to work some of that into the lessons.
You will have to take some time to learn about the team you will be training: Are they distributed? Do they all work together? Are they already working with the thing you will train them on? Are they building line of business software? Are they being rented out to third partys? All of this will influence what the team and what management expect to get out of you, and therefore what you whould deliver. Be ready to manage expectations from both ends.
Does it sound like a lot of work yet? This is just the start.
TL;DR be prepared for pathology on your first engagement. Charge more.