3A = 2.3.3 + 3.4.3 + 4.5.3 + ... + 99.100.3
3A = 2.3.(4-1) + 3.4.(5 -2) + 4.5.(6 - 3) + ... + 99.100.(101 - 98)
3A = 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + 4.5.6 - 3.4.5 + ... + 99.100.101 - 98.99.100
3A = (2.3.4 + 3.4.5 + 4.5.6 + ... + 99.100.101) - (1.2.3 + 2.3.4 + 3.4.5 + ... + 98.99.100)
3A = 99.100.101 - 1.2.3
3A = 999900 - 6
3A = 999894
A = 999894 : 3
A = 333298