Вы можете использовать subset
subset(df, (Col_A - Col_C) <= 100)
# User Col_A Col_B Col_C
#2 b 1450 1450 1440
#3 c 1320 1280 1225
#5 e 1295 1250 1200
#6 f 1295 1295 1250
#8 h 1295 1295 1260
#9 j 1295 1295 1260
#10 k 1295 1295 1260
#12 m 1295 1295 1260
#13 n 1250 1250 1220
#14 o 1200 1200 1160
#16 q 1030 1030 990
Или с filter
dplyr::filter(df, (Col_A - Col_C) <= 100)
data
df <- structure(list(User = structure(1:16, .Label = c("a", "b", "c",
"d", "e", "f", "g", "h", "j", "k", "l", "m", "n", "o", "p", "q"
), class = "factor"), Col_A = c(1450L, 1450L, 1320L, 1300L, 1295L,
1295L, 1295L, 1295L, 1295L, 1295L, 1295L, 1295L, 1250L, 1200L,
1180L, 1030L), Col_B = c(1450L, 1450L, 1280L, 1300L, 1250L, 1295L,
1240L, 1295L, 1295L, 1295L, 1295L, 1295L, 1250L, 1200L, 1180L,
1030L), Col_C = c(1250L, 1440L, 1225L, 1190L, 1200L, 1250L, 1000L,
1260L, 1260L, 1260L, 1190L, 1260L, 1220L, 1160L, 1070L, 990L)),
class = "data.frame", row.names = c(NA, -16L))