The ratios 3:9, 4:12, 5:15, and 6:18 are a pattern of equivalent ratios in the table below.

A multiplication table. In the row labeled 1, the numbers 3, 4, 5, and 6 are highlighted. In the row labeled 3, the numbers 9, 12, 15, and 18 are highlighted.

Which is another ratio in this pattern?
3:1
6:12
7:21
24:27