Pakai cara yaa, terima kasih

Dik: 5 lampu (setiap kamar ada) 15watt, 2 lampu (teras & ruang tamu) 25watt, 1 lampu (ruang tengah) 25watt, 1 lampu (dapur) 20 watt, dan 2 lampu (kamar mandi) 10 watt menyala 7 jam perhari
Dik: daya yg digunakan dalam 1 bulan

5 lampu = 15watt × 5 × 7jam = 525 watt
2 lampu = 25watt × 2 × 7jam = 350 watt
1 lampu = 25watt × 1 × 7jam = 175 watt
1 lampu = 20watt × 1 × 7jam = 140 watt
2 lampu = 10watt × 2 × 7jam = 140 watt
total = 1.330 watt
jadi perbulan = 1.330 × 30
                      = 39.900 watt atau 39,9 kWh
semoga membantu.