Help with formula Sum IF i think ?

edited 12/09/19 in Smartsheet Basics

Hi I Am after some help getting a column of numerals to add only if certain criteria in a drop box are met  

say if Column A was made up all of the number 2 and Column B i had drop box criteria of "Complete"

If i marked Column B "complete" my value would be 2 if i mark 4 Rows in Column B "Complete" my total would be 8 

Any help with this would be amazing 

Thanks in advance