or
c4=IF(OR(COLUMNS($C4:C4)=1,AND(B3>0,C3=0)),INDEX(C3:$T3,MATCH(1,INDEX((C3:$T3>0)+0,0),0))/MATCH(1,INDEX((C3:$T3>0)+0,0),0),IF(B3=0,B4,C3))
Try this and copy towards right