a + b + c = 3003
b : a = 3 rest 21
b = 3a + 21
c : b = 4 rest 18
c = 4b + 18
c = 4(3a + 21) + 18
c = 12a + 84 + 18
c = 12a + 102
a + 3a + 21 + 12a + 102 = 3003
16a = 3003 - 123
a = 2880 : 16
a = 180
b = 3 * 180 + 21
b = 561
c = 12 * 180 + 102
c = 2160 + 102
c = 2262