Problem 2 Histogram using facet_grid

ggplot(data=mpg, aes(hwy, fill=drv))+
  geom_histogram(alpha=0.5)+
  facet_grid(drv~.)+
  theme_minimal()+
  labs(title="Histogram using facet_grid()", subtitle = "Histogram of Highway Mile per Gallon", caption="Source:mpg")

## `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.