Write the code to compute the acf() plot yourself for the file “Furnas 31 78.txt” from the Exercises folder (DataMarket– Hydrology–Monthly riverflow in cms, Furnas–vazoes medias mensais, 1931–1978)....

Write the code to compute the acf() plot yourself for the file “Furnas 31 78.txt” from the Exercises folder (DataMarket– Hydrology–Monthly riverflow in cms, Furnas–vazoes medias mensais, 1931–1978). Also use the R function acf() for comparison. Since the data is monthly you should compute 4–5 years of lags to check for a persistent periodicity. Is the period obvious in the plot? Explain.