Final answer:
The question pertains to a readonly property in object-oriented programming, and none of the provided options are valid for altering the private dblTax variable associated with the readonly tax property of a Purchase class.
Step-by-step explanation:
The student is asking about a readonly property in an object-oriented programming language, likely C#. If the tax property is readonly, it means it can only be assigned a value once, and cannot be modified. This is typically done within the constructor of the class or with a default value that is given at the time of property declaration. Since dbltax is a private variable, it cannot be directly accessed from outside the class.None of the options given (a. currentSale.tax = 0.08; b. currentSale.dblTax = 0.08; c. currentSale.tax = dblTax; d. dblTax = currentSale.tax.ToString("C2")) are valid. Option a is incorrect because you cannot assign a value to a readonly property. Option b is incorrect because dblTax is a private variable and cannot be accessed directly. Option c is also incorrect because it implies assigning a variable to itself, and it is unclear what dblTax refers to in this context.
Option d is incorrect because you cannot assign a string (result of ToString("C2")) to a variable expected to be a double.The question is asking which of the following is valid in the click event procedure for the purchase class. The options given are:a. currentSale.tax = 0.08;b. currentSale.dblTax = 0.08;c. currentSale.tax = dblTax;d. dblTax = currentSale.tax.ToString("C2")The correct answer is option a. currentSale.tax = 0.08; because the tax property in the purchase class is a readonly property, meaning it cannot be directly assigned a value. Only option a assigns a value to the tax property.