please answer the question "without using excel sheet" and do it step by step

A logistics company has been in business for three years and wants to develop quarterly indices. Inventory quantities for each quarter in these years and the quarterly indices are shown in the below table. Assuming that the annual inventory quantity for year 4 will be 267 units. Use seasonal index formula of forecasting and calculate Forecast for Quarter 1 of year 4. Note: Write the answer in round figure Inventory Quantities Quarter Year 1 Year 2 Year 3 Average yearly demand Average quarterly demand Seasonal Index Quarterly demand forecast 1 50 60 40 50 60 0.83 ??? 2 70 80 60 70 60 1.16 3 90 80 70 80 60 1.33 4 40 50 30 40 60 0.66