Comet cable charges $32.50 a month for basic cable television. Each premium channel selected costs an additional $4.50 per month. Write an expression to find the cost per month

32.50+4.50x

You are going to pay $32.50 no matter what, that is what you pay for basic cable. $4.50 is what you pay for the extras, so depending on how many premium channels you want, you will pay $4.50 for every extra channel, which is why it is 4.50x because the x is how many premium channels you purchase that month.