Substitute x=3 into 3x-x²

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

Evaluate the expression for the given value of the variable 7a - 4a for a =8

How to solve a simultaneous equation involved with fractions?