So, first let's convert 3 minutes into seconds. We get that 3 min = 180 seconds.
Now, it says that the treasure sinks 20 feet per second and we want to know if it will reach -4,200 feet before 180 seconds. So, one way we can solve that it multiply 180 times 20.
We get 3,600 which means that in 3 minutes, the treasure will be -3,600 feet deep. The treasure will NOT reach the ocean floor in less than 3 minutes.
and 
. Then
(the part of the sphere above the cone) is given by