How do you solve algebraically 8x^2=18

The diameter of a circular chip is doubled to use in a new board game. the area of the new chip will be

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

For f(x)=2x+3 and g(x)=x^2- 8 find (f+g) (x)