hello all,

i have over 100 set data and looking some sum formula with 2 criteria :

a-------6-------x1
b-------3-------x2
b-------2-------x2
b-------7-------x2
a-------6-------x1
c-------9-------x3
a-------10-------x1
c-------4-------x3
d-------7-------x4
etc....

how to sum data number not include/ignore x1 and x3

thanks!!