Answer:
It is after 4 explorations that the submarine's elevation would have changed by -3/2 miles
Step-by-step explanation:
From the question,
The elevation of the submarine changes by -3/8 mile after each exploration.
To determine the number of explorations it will take for the submarine's elevation to have changed by -3/2 miles, we will divide -3/2 miles by the number of miles the elevation of the submarine changes per exploration (that is, -3/8 mile),
That is,
-3/2 miles ÷ -3/8 mile
= 
= 
=
= 4
Hence, it is after 4 explorations that the submarine's elevation would have changed by -3/2 miles.
Answer:

Step-by-step explanation:
Given
--- Average
--- Average
Required
Determine the overall average
Represent the sum of the first three with x.
So:

Solve for x


Represent the sum of the next seven with y.
So:

Solve for y


The overall average is calculated as thus:



