In this lab, you write a C# program as follows:

$$ Create a program that calculates the final bill of a customer after discounts.

$$ Follow the Console $($below$)$ for a sample run.

Specifications

Use decision structure in your solution.

Consider the case the user enters an invalid letter $($other than A or B$)$ in which the program displays a message to warn the user of the invalid entry then the program exits.

The formulas to calculate the final bill for customers A and B:

Customer A: bill $=$ purchase amount $-($purchase amount $*0\mathrm{.}35)+($ purchase amount $*0\mathrm{.}13)$

Customer B: bill $=$ purchase amount $-($purchase amount $*0\mathrm{.}25)$