Let 3pm equal max height =100%
Level drops by 10% =2 feet
So, 100% = 20 feet.
Now at 4pm level has dropped by 10% to 90% = 20x0.9 = 18 feet
On the day of a rainstorm, the depth of the water at a certain location along the Winding River was recorded hourly, and the results are indicated in the line graph above. Each unit on the vertical axis represents 1 foot. If the depth of the water decreased 10 percent from 3:00 P.M. to 4:00 P.M., what was the depth of the water at 4:00 P.M.?