Prove, using a combinatorial (counting) argument, that c(2n, 2) = 2c(n, 2) + n 2

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

Three times the sum of a number and seven is negative thirty-six. what is the number?

Solve 4 ln x=2ln25 a) x=5 b) x=25 c) x=625