You may find something here useful, but yes, posting a reprex makes it much easier for people to help.
latex2exp::TeX Converts a LaTeX string to a plotmath expression.
library(ggplot2)
library(latex2exp)
c. <- -824
m. <- 1608
r2. <- 0.6
eq <- TeX(paste0("$y = ", c., " + ", m., "\\cdot x, r^2 = ", r2., "$"))
ggplot() +
geom_text() +
annotate(
"text",
label = eq,
x = 4,
y = 30,
size = 5,
colour = "darkblue"
)

Created on 2019-01-11 by the reprex package (v0.2.1)