Ending sounds are usually more difficult to hear than beginning sounds, so you may need to help him with the ending sounds for a bit. But I would also encourage you to do a lot of review to make sure each step is taken on firm ground. You can use the list of activities and games in the back of the book to get more ideas for reviewing the words you have already covered.
Richele might chime in here, but as far as “how quickly” he should solve the equations, Book 1 is all about discovery and exploration and comprehending how math works. It is not about speed. Watch for understanding instead. If he seems to have a good grasp on the math concepts you are working on, go ahead and move on. If he’s confused or waits for your helpful prompts and reminders, you may want to slow down and do some review. In math, as well as reading, you want to secure the ground under each step.