A recently formed computer software company bought 100 computers at the rate of *30,000 per computer, on September 6, 2011, and put them to immediate use. Soon thereafter, a new generation of computers got introduced in the market. The newer computers were far more useful for the kind of work the software company was doing. The company decided to start using the new generation computers. Towards this, it sold off 50 of its computers at the rate of 20,000 a computer, in February, 2013. Work out the written down value for the assessment years, 2012-13, 2013-14 and 2014-15.