Answer:
the blank would be 640
Step-by-step explanation:
I'm just going to assume this is a question where you have to complete the pattern
Every time a new number is added, the number is one less then the one before.
I know that makes 0 sense so here:
610+9=619
619+8=627
627+7=634
634+6=640
640+5=645
So 640 would be the only one that makes sense
I hope I was correct and I helped you out!