The ggmsic package makes this fairly simple.
Df <- data.frame(JAR = seq(20, 60, 5),
Flavor = c(3, 4.5, 4.9, 6, 7.2, 7.8, 8.3, 8.6, 8.9))
library(ggplot2)
library(ggpmisc)
ggplot(Df, aes(x = JAR, y = Flavor)) +
geom_point(color = "#669999") +
geom_smooth(method=lm, linetype = "dashed", color="black") +
coord_cartesian(ylim=c(1, 10)) +
scale_y_continuous(breaks=seq(1, 10, 1)) +
stat_poly_eq(formula = y ~ x,
aes(label = paste(..eq.label.., ..rr.label.., sep = "~~~")),
parse = TRUE)
#> `geom_smooth()` using formula 'y ~ x'

Created on 2020-07-06 by the reprex package (v0.3.0)