Answer:
B. -6.5
explanation:
Basiclly what the person above said, to find the common number, subtract two numbers together. After it gives you the common ration, prove the answer it gives you by adding the common ration with a number in the sequence to give you the number before, example:
9 - 2.5 = 6.5
6.5 + 2.5 = 9
Hope it helps!