have to do R coding in r studio

Use the mts petrol to answer the following questions.

a$.$ Using the backwards stepwise method, starting with a model that contains Chemicals,

Coal, Vehicles, trend, season, trading days, and an intervention spike for the oil crisis

that lasted from October $1973$ Through December $1974,$ determine the Time Series

regression model that best predicts Petrol sales.

b$.$ Now use a forward stepwise method. Did you end with the same model?

c$.$ Forecast for $12$ periods the model$($s$)$ you arrived at from part $($a$)$ and $($b$)$ using ets

forecasts of the predictor variables and plot them.

d$.$ Add to that plot two scenario forecasts, one where vehicle sales double to $40,$ and

another where they shrink to $10.$ Keep your forecasts of the other variables the same.

Plot the resulting forecasts of Petrol.