Help with hard Math

[Guest]

A 158 lb person runs on a horizontal wet surface at 3 mph before decelerating to 1.5 mph about 4 feet before a right turn. There are cement stairs at the turn that he plans on using to enter a home. Before he gets to the turn he slips (at this point his right foot has made it onto the cement, whereas his left foot is still on the grass). As he slips he is facing forward on the horizontal surface and his body weight shifts erratically forward onto his right side...which results in a fractured lower right fibula and ankle. Let’s assume that the fractural load level for this person to sustain a foot-ankle fracture is 11 N. The injury resulted in a closed, spiral fracture.
(1) List and estimate the forces involved.
(2) Also list the force involved when compared to the injury tolerance of 11N.

I already figured some things out on my own, such as the fracture load levels etc. I can actually place more assumptions into this story if I need to, so if more info is needed to answer questions 1-2 feel free to add in your own assumptions. I'm doing a biomechanical reconstruction of an accident of my choosing. The only things that are known are the things that I've already placed into the story, so more assumptions can be added so long as it doesn't conflict with the data I already presented in the story.
But here's where I'm stuck: I'm stuck on the part where I need to find the friction force involved, in order to answer questions 1-2. I copied/pasted the instructions on how to find the friction force below. I hope they apply to my question though. I need to know if they don't apply. I also need to know if the information I have is good enough to anser questions 1-2 and if not can the experts add their own assumptions into the story?

To find the friction force you need to first find the coefficient of friction, which is equal to tan(θ), where θ is the angle from the horizontal where an object placed on top of another starts to move. For a flat surface, you can pull an object across the surface with a Newtonmeter attached. Divide the Newtons required to move the object by the object’s mass to get the coefficient of friction.

Is this the right formula to find the friction force? Can someone give me a better formula because this one is really confusing???

[sueambrose121]

I tried to solve this problem and didn't figure it out too, unfortunately.