Trains travelling long distances have two additional first class carriages which are laid out differently. The carriage is the same size and has the same exit sections at each end, but each passenger gets an individual seat $($there are no separate luggage areas or tables$).$ The carriage has three seats per row, separated by $2$ aisles. Each seat requires $1\mathrm{.}5\mathrm{????}$ of length along the carriage. How many more seats does a train travelling long distance have?