[(20113a : 4) * 7 - 2000] : 3 - 661000 = 1000
[(20113a : 4) * 7 - 2000] : 3 = 661000 + 1000
[(20113a : 4) * 7 - 2000] = 662000 * 3
(20113a : 4) * 7 = 1986000 + 2000
20113a : 4 = 1988000 : 7
20113a = 284000 * 4
20113a = 1136000
a = 1136000 : 20113
a = 56,48