a$)$ How do seasonal variations or fluctuations differ from cyclical variations? How does Time$-$Series Decomposition $($TSD$)$ help an Operations Manager$/$Statistical Analyst $/$Industrial Engineer who is primarily interested in forecasting the future values of a variable where seasonal variations are present in the data $?$

b$)$ What is the value of the Mean Absolute Deviation $($MAD$)$ for the following data $?($Remember that only absolute values of differences between actual data values and forecasted values are relevant for calculating MAD$)$; why is the MAD not used extensively in real$-$world calculations of forecasting deviations or errors $?$