In order to check if the sequence is arithmetic or not, we need to subtract each number by the number before and check if this ratio is always the same. So we have:
27 - 12 = 15
42 - 27 = 15
57 - 42 = 15
72 - 57 = 15
The ratio is always 15, so this sequence is arithmetic, therefore the correct option is the first one.
