Final answer:
Using the rules of significant figures, the correct answer for the equation 23.6 - 4 is 19 (choice d), as it matches the least decimal places of the numbers involved in the subtraction.
Step-by-step explanation:
The question pertains to subtracting two numbers while considering the rules of significant figures. In the equation 23.6 - 4, we need to determine the correct answer following these rules. When subtracting, the result should have the same number of decimal places as the number with the least number of decimal places in the original problem. Since 4 has no decimal places, the result should also have no decimal places.
Therefore, given the options, the correct answer is 19. Answer choice (d) is correct because it has no decimal places, matching the least precise measurement (which is 4, with zero decimal places).