Answer:
Unit rates for cyclist A , B, C , D are 12 mile/ hour , 5 mile/hour, 9 mile/hour and 10 mile/hour respectively. Cyclist A is the fastest among the four. 
Step-by-step explanation:
Cyclist A can ride 24 miles in 2 hours
so, cyclist A's  unit rate is, 
                                        = 12 mile/hour
Cyclist B's unit rate is, 
                                  = 
                                  = 
                                  =  5 mile/hour
Equation for cyclist C is, y = 9x , 
so, cyclist C's unit rate is , 9 mile/hour
Slope of the graph for cyclist D,
 = 
  = 10
So cyclist D's unit rate is, 10 mile/hour
So, cyclist  A is the fastest.