TimeSeries ARIMA

Hello everybody, i really need help on this one. I have to forecast sales using ARIMA and i have no problem with that. But the issue is, i have to make a prediction of futures sales knowing already the price and if exists promotion or not. The dataset is something like this
sales Price Promotion Data
1 4552.172 1.5 No 2015-01-01
2 5370.789 1.5 No 2015-02-01
3 10204.838 1.2 No 2015-03-01
4 12368.806 1.5 No 2015-04-01
5 12521.396 1.5 No 2015-05-01
6 3917.904 1.5 No 2015-06-01

... ... .... ....
With this i have to predict the sales for 2019-01-01 knowing the price is 1.40 and exists promotion.
How can start this? should i start forecasting the sales?
Thank you for the help

Have a look at chapter 9:

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