Answer:
42 ft
Step-by-step explanation:
[tex] - 120 + 13m \\ = - 120 + 13 \times 6..(plug \: m = 6 )\\ = - 120 + 78 \\ = - 42 \: ft[/tex]
(Negative sign symbolises that the submarine is below the sea level or depth of the submarine.)
Hence, the depth of the submarine after 6 minutes was 42 ft.