### Problem 4 HW3.. please key in the answer. not pictures Levels of carbon dioxide ($CO_2$) in the atmosphere are rising rapidly, far above any levels ever before recorded. Levels were around 278 parts per million (ppm) in 1800, before the Industrial Age, and had never, in the hundreds of thousands of years before that, gone above 300 ppm. Levels are exceeding 400 ppm. The dataset CarbonDioxide (http://www.lock5stat.com/datasets/CarbonDioxide.csv) shows the rapid rise of $CO_2$ concentrations over the last 50 years.

a) What is the explanatory variable? What is the response variable?

b) Draw a scatter plot of the data. Does there appear to be a linear relationship in the data?

```{r} CO_2=read.csv("http://www.lock5stat.com/datasets1e/CarbonDioxide.csv") ```

c) Find the correlation between year and $CO_2$ levels. Does the value of the correlation support your answer to part (b)?

```{r} # Insert R code here

```

d) Calculate the least-square (regression) line to predict $CO_2$ from year.

```{r} # Insert R code here ```

e) Interpret the slope of the regression line, in terms of carbon dioxide concetrations.

```{r} # Insert R code here

```

f) Use the regression line to predict the $CO_2$-level in 2020.

```{r} # Insert R code here ```