6 Time différence n and 15

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

Which one ? is the answer and how to find this answer

One of every 20 customers reports poor customer service on your company’s customer satisfaction survey. you have just created a new process that should cut the number of poor customer service complaints in half. what percentage of customers would you expect to report poor service after this process is implemented? 1.) 5% 2.) 10% 3.) 2% 4.) 2.5%