(X-1):3=(20-2x):3
3x-3=60-6x
3x+6x=60+3
9x=63
x=63:9
x=7
1) 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30
2) 1, 2, 4, 5, 8, 10, 16, 20, 40
3) 6, 12, 24, 30
4) 10, 20, 30, 40