Final answer:
To write this program, use Python to accept a whole number, multiply it by 21, and output the product.
Step-by-step explanation:
To write a program that accepts a whole number as input, multiplies it by 21, and then outputs the product, you can use a programming language like Python. Firstly, you need to take user input as a string and convert it to an integer to ensure it is a number. Then, you can multiply the input by 21 and display the result. Here's an example:
number = int(input('Enter a whole number: ')) product = number * 21 print('The product is:', product)
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