First of all thank you very much for sparing your precious time to check this solution.

A- I prepared it in organized form on a MS office page with proper table insertion but during copy pasting something went wrong even after posting here I was unable to take its proper understanding anyways hats off to you that you still manage to read hahahaha. But thank you thank you so much.
Ya you are right that it should be like Depreciation rate = ¼ x 2 = 50% actually I try to be sophisticated and presentable with proper formulas (even though I failed badly later) anyways yes you are right that i should work smartly and save time n next time I will do the same.
C-When depreciation is charged
In B.Com books entry is like (Accounting by M Arif & Sohail Afzal)
Depreciation a/c …………..Dr
Asset a/c………………….Cr
In M.com entry is like
Depreciation a/c …………….Dr
Accumulated depreciation …..Cr
At the disposal of asset
Accumulated depreciation …..Dr
Asset a/c ……………………Cr
Any ways next time I will follow latter.