subFord <- subset(ford, ford$co2_emissions <= quantile(ford$co2_emissions, 0.75))
subDaimler <- subset(daimler, daimler$co2_emissions <= quantile(daimler$co2_emissions, 0.75))
subGM <- subset(gm, gm$co2_emissions <= quantile(gm$co2_emissions, 0.75))

manufacturer <- c('ford', 'daimler', 'gm')

for(i in manufacturer) {
paste('sub', i, sep = '') <- subset(i, i$co2_emissions <= quantile(i$co2_emissions, 0.75))
}

assign(paste('sub', i, sep = ''), subset(i, i$co2_emissions <= quantile(i$co2_emissions, 0.75)))