I don't know what a "T-chart" is, but I can help you with the factors of 21 and 57.
21 = 3*7, so it is divisible by 1, 3, 7, and 21.
57 = 3*19, so it is divisible by 1, 3, 19, and 57.
21 = 3*7, so it is divisible by 1, 3, 7, and 21.
57 = 3*19, so it is divisible by 1, 3, 19, and 57.
