Need help with this problem please Find the prognosis for 20

Need help with this problem please:

Find the prognosis for 2012 using the tendencies method in series of time. Period     Demands
2007           200
2008          150
2009          125
2010          100
2011            50

Problem: Find the prognosis for all the possible periods N=3, using the information and the method of movable averages.