EDITED TO USE A QUARTERLY SERIES/MODEL
I took quarterly series (in logs) and estimated your model and obtained . I also asked for a pure right hand side ( regression form ) version and obtained This second form is usable by "beginners" in time series as it often clears up the fog and aids understanding/comprehension. A third way is to restate the ARIMA model as a PDL/ADL in the history of the series since ARIMA models are simply optimal weighted averages of the past. You can (in this case ) obtain those weights (coefficients of the past) by dividing [1-B4] by [1+.727B1][1-.708**4]. These are called the pi weights . Thus the question "How many values should I use in my weighted average and what weights should I apply" is answered by ARIMA.
See Seeking certain type of ARIMA explanation for a more detailed discussion of the equivalence of ARIMA and weighted averages.