For it to double in value it would take 13 years and 4 months
Answer: 8.55 feet
Step-by-step explanation:
We should equal the average depth to 1, so if it raises 3%, it raises 0.03. Simply add the original (1) plus what it rose (0.03) and multiply the original by that, so 8.3 × 1.03 = new depth. The result is 8.549 feets.
The figure on the top left is a triangle with base 11 and height 8, for an area of

Immediately below, we have a rectangle with dimensions 11 and 9, for an area of

Moving to the right, we have a parallelogram with base 9 and heght 11, which again has height

Finally, the rightmost figure is a triangle with base 8 and height 9, for a total of

Sum these areas and you'll get the total area