The way I have found to remember it correctly is this:
1. a one-inch rise in 100 horizontal inches of track is a 1% grade.
2. If you want a 3% grade, that means that, as it goes forward 100 inches,
it rises 3 inches.
So, for a 9.6% grade, your locomotive is going up 9 1/2 inches as it goes forward 100 inches (8.3 feet). That is a mighty steep climb. To put it into perspective, going from left to right, your first 10" track has the left end on the ground and the right end 1" in the air. Track #2 starts at 1" in the air and at the far end is 2" up, and so on. Most people go with a 3% grade as a good ballpark figure that a locomotive can pull a train up successfully.