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 : -10
This creates the following sequence: [5, -5, -15, -25, -35]
The following transformation applies to the sequence for the numerators: -3
This creates the following sequence: [7, 4, 1, -2, -5]
Take a good look at how to rewrite the fractions in the series to recognize the pattern.
For example, 25/2 can be rewritten as -25/-2