$$

Moving average and weighted moving average

Sales of hair dryers at the Walgreens stores in Youngstown, Ohio, over the past $4$ months have been $100,110,120,$ and $130$ units $($with $130$ being the most recent sales$).$

Develop a moving$-$average forecast for next month, using these three techniques:

a$)3-$month moving average.

b$)4-$month moving average.

c$)$ Weighted $4-$month moving average with the most recent month weighted $4,$ the preceding month $3,$ then $2,$ and the oldest month weighted $1.$

d$)$ If next month's sales turn out to be $140$ units, forecast the following month's sales $($months$)$ using a $4-$month moving average.