Answer: 270 ft
Explanation:
If the depths increase by 30 for every 1 atmosphere of pressure, and the sub starts at 0 ft with 30 atmosphere of pressure, then to find the answer, add 30 to the depth starting with 30 at an atmosphere of 2. With 3 atmosphere, the depth is 90. Hopefully I explained it right and got the correct answer. If not, I tried my best.