Meter No.
=AND(LEN(B4)=5,COUNTIF(B4:B11,B4)<2)

Consumed Unit
=F4-E4

Bill
=IF(G4<=75,G4*4.75,IF(G4<=125,G4*5.2,IF(G4<=150,G4*5.5,IF(G4<=250,G4*6,IF(G4<=400,G4*6.5,G4*7)))))

Vat
=H4*2%

Total
=SUM(H4:J4)

MAX/MIN
=MIN/MAX(K4:K11)