I need help!!!

Does anyone know how to solve the following:
7 _ _ _ _ 77 ?

I have to find the missing values.

Is there a formula for this? Can it be used for any amount of missing values? I'd appreciate any help. I am in fifth grade, ten years old and driving my Mom nuts!!!

Thank you, Peter

Sure there are ways. The trick is to look NOT at how many _'s there are (four) but at how many GAPs there are between the _'s and the end numbers.. The suggestion, as I understand it, is that these GAPS should all be the same length. The distance from 7 to 77 is 77 - 7 = 70 and 70 divided into 5 equal sized GAPS gives GAPS of size 70/5 = 14.