In this sequence there are actually two sequences. 1 sequence for the numerators and one sequence for the denominators. The following transformation applies to the sequence for the denominators : +6
This creates the following sequence: [-10, -4, 2, 8, 14, 20]
The following transformation applies to the sequence for the numerators: -3
This creates the following sequence: [2, -1, -4, -7, -10, -13]
Take a good look at how to rewrite the fractions in the series to recognize the pattern.
For example, -5/1 can be rewritten as -10/2