The Four-Quadrant Model

CAIA
#1

Can someone explain this answer to me from TestBank of Uppermark?

"If there is no change in the stock of space in the southeast quadrant of the four-quadrant real estate model, which of the following most accurately represents the amount of stock of space?

Answer: construction C divided by depreciation rate d

Explanation: When change in stock of space S is zero (i.e., DS = 0), then S = C/d."

I dont understand why we are dividing the Construction with the depreciation rate.

#2

It’s down to the given formula:

Change Stock of Space = Construction - (Depreciation x Amount of Stock of Space)

Change S = C - dS

If Change S = 0 then…

0 = C - dS

dS = C

S = C/d