a cyclist and her bicycle have mass 75kg. she is riding on a horizontal road, and positions herself so that 60% of the normal contact force is on the back wheel and 40% on the front wheel. The coefficient of friction between the tires and the road is 0.8. What is the greatest acceleration she can hope to achieve?

Whilst riding at 6ms^-1, she applies both brakes to stop the wheels rotating. In what distance will she come to a stop?

My big problem here is I don't know which forces i am dealing with and what their directions are. I know how to calculate frictional force but i dont understand how I can solve these problems without knowing the force she applies to move the bicylce forward.