L x w x h = volume
volume = 5 x 5 x 5 = 125 cm ^ 3
Total length of the fabric is 
We need to find the number of scarves can she make if she needs 5/6 of a yard for each scarf.
Let she needs x scarves. So, ATQ
Hence, she can make 8 scarves.
To answer b - You need to find how much it costs to rent a bike per hour. To do this divide the over all cost ($12) by your amount of time (3 hrs) to get $4 per hour. Same with the $20 per 5 hours!
The answer to your question is 0.0032