Answer: The initial elevation of the plane was 8.75 miles.
Step-by-step explanation:
Suppose that the initial elevation of the plane is E.
Then the plane descends 3.5 miles.
Then the new elevation of the plane will be:
E - 3.5 miles.
Now, we know that the new elevation of the plane is 5.25 miles, then:
E - 3.5 miles = 5.25 miles.
Now we need to solve this for E.
To solve this, we can add the same number to both sides of the equation, so we can add 3.5 miles to both sides to get:
(E - 3.5 miles) + 3.5 miles = 5.25 miles + 3.5 miles
E + (3.5 miles - 3.5 miles) = 5.25 miles + 3.5 miles
E = 8.75 miles.
The initial elevation of the plane was 8.75 miles.
