I need help with these math exercises. I already did them alone that I don’t know if they are correct.

Apublic library wants to place 4 magazines and 9 books on each display shelf. the expressions 4s +9s represents the total number of items that will be displayed on s shelves. simplify this expression

Determine the mean and variance of the random variable with the following probability mass function. f(x)=( 729divided by 91) (1 divided by 9) superscript x baseline comma x equals 1,2,3 round your answers to three decimal places (e.g. 98.765).

Each cookie sells for $0.50 sam spent $90 on baking supplies and each cookie cost $0.25 to make how many cookies does sam need to sell before making a profit formula: sales> cost