With a certain medical insurance policy, the customer must first pay an annual $250 deductible, and then the policy covers 70% of the cost of x-rays. The first insurance claims for a specific year submitted by a person are for two x-rays. The first x-ray cost $630, and the second x-ray cost $910. How much, in total, will he need to pay for these x-rays?

Time = 25/9 hr

Step-by-step explanation:

Let speed of boat in still water is x km/hr

then, speed in downstream equals to "x + 3"km/hr

and speed in upstream equals to "x - 3" km/hr

We also know that time taken to travel 3km in upstream is twice as time taken to travel 4km in downstream.

so,  using time = distance/speed

              3/x- 3   = 2 × (4/x + 3)

                3x + 9 = 8x -24

                    5x = 33

                      x = 33/5 km/hr

Net speed in upstream = 33/5 - 3 = 18/5 km/hr

So, Time taken to travel 10km upstream = distance /speed

                      =  (10 × 5) / 18 = 25/9 hr

Time = 25/9 hr