By Indirect method which you used above each Asset item decrease is the cash flow increase while Liabilities increase means CF increase and vice versa.
In general, it can be easy to understand by folllowing rule + an asset (f.ex.purchase) - cash flow (spent) and - an asset (f.ex.sold) + cash flow (earned).
If your asset price change was positive in current year compared to previous year (45 K in this example) your cash flow would change in opposite direction, thus you will realize -5K instead +5K on BS change.
Applying this logic to the first scenario when land price decreases to 35k from 40k we get CF incr of 5k and gain of 10k so the gross cost of land sold is 15k but it is should be 5k according to soln … what am i missing??
Assume simply that durig year you got inflows and outflows which is real situation at each company in the world. In this example, you have made some purchase particles of land and selling another particles. Each BS and P/L change in this activity reflects on CF.