A scientist uses a submarine to study ocean lift. She begins at sea level, which is at an elevation of 0 feet.
She travels straight down for 1 ½ minutes at a speed of 3.6 feet per second.
She then travels directly up for 30 seconds at a speed of 2.4 feet per second.

After this 120-second period, how much time, in seconds, will it take for the scientist to travel back to sea level at the submarine’s maximum speed of 4.2 feet per second?

A
15.9 seconds

B
60 seconds

C
76.9 seconds

D
77.1 seconds