Explanation:

To convert 5 3/4 to a decimal, divide the numerator (3) by the denominator (4) to get 0.75. Adding this to the whole number 5 results in 5.75. When rounding to the nearest tenth, 5.75 rounds to 5.8. Choice A, 5.75, is the exact conversion before rounding, so it is incorrect. Choice B, 5.7, is incorrect because it does not account for the 0.05 difference when rounding. Choice C, 6, is incorrect as it is the closest whole number but not a decimal approximation. Therefore, the correct answer is 5.8.