Sum of the decimal places = 7 .Since the last digit to the extreme right will be zero ( 5 * 4 = 20), so there will be 6 significant digits to the right of the decimal point....
Suppose commodity X wil cost 40 paise more than Y after Z years.Then, (4.20 + 0.40Z) - (6.30 + 0.15Z) = 0.40 0.25Z = 0.40 + 2.10 Z= X will cost 40 paise more than Y 10 years after 2001 . i.e in 2011