67 8 but mostly 6 i know it but it's confusing

Sara needs to take a taxi to get to the movies the taxi charges $4.00 for the first mile and then $2.75 for each mile after that if the total charge is $20.50 then how far was sara’s taxi ride to the movie

∆red ≅ ∆ by rule will give brainiest if possible

Pls the last one and it has to be like number 6