With the information provided, we can create the following equation for the position of the sea lion (p)
p = 3x - 10
In this equation, x would be the final position of the seal when it caught the fish. Since we are told that the seal's position is 25 feet below sea level then we can plug in this value as x and solve for p...
p = (3 * 25) - 10
p = 75 - 10
p = 65
Finally, we can see that the sea lion's position is 65 feet below sea level.
