Hi, and welcome.
Please review the FAQ: What's a reproducible example (`reprex`) and how do I do one? This leads to better answers.
Using dplyr on a data frame, to get the count of rows meeting some condition, the filter() function piped to count() will get you a summary like this
suppressPackageStartupMessages(library(dplyr))
(mtcars %>% filter(mpg <= 25 & wt >= 3.500) %>% count())
#> # A tibble: 1 x 1
#> n
#> <int>
#> 1 11
Created on 2020-02-24 by the reprex package (v0.3.0)