"C"&ROW(4:4)*4-12 creates a cell reference for use with indirect function. So if you try =ROW(4:4)*4-12 and drag it down you will see that it change from 4 to 8 and to 12, etc. ROW(4:4)*=16 -12 = 4) The "C" part and number 4 will make C4 and INDIRECT function converts this text into cell reference.
Hope this help.
And I think I found my mistake
It should be this
=(INDIRECT("C"&ROW(4:4)*4-12)+2*INDIRECT("C"&ROW(5:5)*4-15)+3*INDIRECT("C"&ROW(6:6)*4-18))/INDIRECT("C"&ROW(7:7)*4-21)
Bookmarks