Final answer:
To determine the depth of the submarine after 6 minutes, we calculate -120 + 13.4(6), which results in -39.6 feet. The submarine is still 39.6 feet below sea level.
Step-by-step explanation:
To find the depth of the submarine after 6 minutes, we begin with the given expression, -120 + 13.4m. This expression states that the submarine begins at a depth of -120 feet (120 feet below sea level) and ascends at a rate of 13.4 feet per minute. The variable m represents the number of minutes the submarine ascends.
To calculate the depth after 6 minutes, we substitute 6 for m in the expression:
-120 + 13.4(6) = -120 + 80.4 = -39.6
Therefore, the depth of the submarine after 6 minutes is -39.6 feet, meaning it is still 39.6 feet below sea level.