Answer:1
4
Step-by-step explanation:
Original position of the submarine below the Surface = -2 2/3= -8/3
Submarine at a depth of -2 2/3 feet descended by 5 1/2 feet.
So new position of the Submarine = 
To Reach the surface submarine must rise = 0-(-49/6)
As seen from the equation the two negative sign [(-)(-)] will change into a positive sign.
At the surface the position of the submarine = +49/6 feet
We want to use elimination to solve
y = 0 (1)
x + y = 40 (2)
Multiply (1) by -1 to eliminate y.
-y = 0 (3)
Add (2) and (3).
x + y + (-y) = 40 + 0
x = 40
Answer: Multiply by -1.