The Formula S_t = Wy_t + (1 - W)S_t-1 Is

The formula S_t = wy_t + (1 - w) S_t-1 is used in time-series forecasting with exponential smoothing,where S_t is the exponentially smoothed time series at time t,y_t is the value of the time series at time t,and w is the smoothing constant.The forecasted value at time t + 1 where w = .4 is given by:

A) F_{t + 1} = 0.4y_{t +1} + 0.6S_{t + 1}
B) F_{t + 1} = 0.4y_t + 0.6S_t
C) F_{t + 1} = 0.4y_t + 0.6S_{t - 1}
D) F_{t + 1} = 0.4y_{t - 1} + 0.6S_t