Answer:

So then it takes 2 minutes to reach the surface from a 120 foot dive,
Explanation:
For this case we can define some notation
represent the distance ascend
represent the time to reach the surface
For this case we know that it takes 0.75 minutes to reach the surface from 45 ft foot dive. That represent the info known.
And we want to find how much time b is required to rach the surface from a 120 foot dive. So we can use the following proportion:

And if we solve for b we got:

So then it takes 2 minutes to reach the surface from a 120 foot dive,