A submarine cruising underwater started diving at a rate of 9 meters per minute. after 5 minutes, it was 180 meters below the surface of the water. how long after starting its descent was the submarine 360 meters below the surface?

Diving rate = 9 m/min

Let h = original depth, m

After 5 min, the depth is 180 m. Therefore

h + (9 m/min) * (5 min) = (180 m)

h + 45 = 180

h = 135 m

Let t min = time to reach a depth of 360 m.

Then

135 + (9 m/min) * (t min) = 360

9t = 225

t = 25 min

Answer: 25 minutes