a.1990.1990-1992.1998
= 3960100 - 3980016
= -19916
b.[1379.57+687.86] chia [26.13+74.14
= (78603 + 59082) : (338 + 1036)
= 137685 : 1374
= 45895/458
c. 2002.20012001-2001.20022002
=2002.2001.10001-2001.2002.10001
=(2002-2002).(2001-2001).(10001-10001)
=0