How to calculate actual demand. and seasonal factors.

I need help because I am really stuck.

DEMAND Month 2 3 4 5 6 7 8 9 10 II 12 Year 1 55,220 57,350 15,445 27,776 21 ,408 17,118 18,028 19,883 15,796 53,665 83,269 72,991 Year 2 39,875 64,128 47 ,653 43,050 39,359 10,317 45,194 46,530 22,105 41 ,350 46,024 41 ,856 Year 3 32,180 38,600 25,020 51 ,300 31 ,790 32, 100 59,832 30,740 47,800 73,890 60,202 55,200 Year 4 62,377 66,501 31 ,404 36,504 16,888 18,909 35,500 51 ,250 34,443 68,088 68,175 61,100