For this case we have that the generic equation of the line is given by:

Where,
m: slope of the line
b: intersection with the y axis.
Since the line is parallel to PQ, then the slopes are equal.
We have then:

On the other hand we have:

Substituting values we have:
Answer:
The equation of the line that is parallel to line PQ and that has the and intercept b = -3 is:
-6 - 3 = -9
12 - (-6) = 18
4 - 12 = -8
20 - 4 = 16
The first difference is -9. The third difference is -8.
Maybe the fifth difference is -7.
That makes the next term 13.
<span>3, -6, 12, 4, 20, 13</span>