Ответ 1
будет ли это работать для вас,
# install.packages("ggplot2", dependencies = TRUE)
require(ggplot2)
DF <- data.frame(x = rnorm(400))
m <- ggplot(DF, aes(x = x)) + geom_histogram()
m + labs(title = "Vehicle \n Weight-Gas \n Mileage Relationship \n
and some really long so that you can seee it centered") +
theme(plot.title = element_text(hjust = 0.5))
извините за опечатки в заголовке сюжета...