Answer:
The submarine is at 67 feet below the sea level (-67)
Explanation:
* Lets explain how to solve the problem
- The zero level is the sea level
- Any height below the sea level is negative
- Any height above the sea level is positive
- A submarine starts out at 135 feet below the sea level
∴ The submarine is at -135 feet
- The submarine dives 239 feet before rising
∴ The submarine dives another -239
∴ The submarine is at -135 + -239 = -374 feet
* The submarine is at 374 feet below the sea level
- The submarine rising 307 feet
∴ The submarine dives 307 feet up
- Add the last position to the rising distance
∴ The current depth of the submarine = -374 + 307 = -67 feet
∴ The submarine is at 67 feet below the sea level