Suppose you are given the following ARIMA(1,0,1) model:

Y(t) = 0.0 + 1.0Y(t-1) + e(t) - 0.5e(t-1)

Assume that t is the year 2009, and that Y(t) = 27. The predicted value for Y(t) = 27.5

Calculate a value for e(t).