What is the amount of subscription for the year 31st March 2020 still in arrears?

₹6,000

The correct answer is option 3- ₹6,000.

Subscription in arrears for the previous year is ₹45,000 out of which 20% is written off
Written off = 45,000 x 90/100
                  = 9,000

So o/s subscription for the year ending 31 March 2020 = 45,000 - 9,000
                                                                                      = 36,000

Out of 36,000, ₹30,000 is received in this year.
So after receiving 30,000, the remaining amount is still in arrears.

Arrears amount = 36,000 - 30,000
                         = 6,000 

Thus, 6,000 is the O/S for the previous year ending 31 March 2020.