How to check differentiability of a piecewise function.

Me because some of question i don’t understand

Steve wants to develop a way to find the total cost of any item including sales tax. the sales tax in his city is 6%. his friend jenna writes the expression x + 6x where x is the cost of the item. explain whether her expression is correct based on the situation.

What is the prime factorization of 23 ?me with this question