please show gormulas and workings

1 Month 2 1/1/2019 2/1/2019 3/1/2019 4/1/2019 5/1/2019 7 6/1/2019 7/1/2019 8/1/2019 163545 8 9 10 9/1/2019 11 10/1/2019 12 11/1/2019 12 12/1/2019 Demand 2324 2789 2442 3020 2379 3482 3362 2635 2274 3271 3575 4355 Yearly average 2992.33 Seasonal Index 0.7767 0.9320 0.8161 Average Sl 1.0092 0.7950 1.1636 1.1235 0.8806 0.7599 1.0931 1.1947 1.4554 Deseasonalized Time period 1 Month 2 1/1/2019 2/1/2019 3/1/2019 4/1/2019 5/1/2019 7 6/1/2019 7/1/2019 8/1/2019 163545 8 9 10 9/1/2019 11 10/1/2019 12 11/1/2019 12 12/1/2019 Demand 2324 2789 2442 3020 2379 3482 3362 2635 2274 3271 3575 4355 Yearly average 2992.33 Seasonal Index 0.7767 0.9320 0.8161 Average Sl 1.0092 0.7950 1.1636 1.1235 0.8806 0.7599 1.0931 1.1947 1.4554 Deseasonalized Time period