The answer should be C- 2 6/7
I believe the question you are asking is what 5 1/4 (otherwise known as 5.25) divided into 15 is.
Simply put, your question is 15 divided by 5.25 (or 5 1/4)
To solve this we can make the fraction 5 1/4 into an improper fraction. This makes the fraction to consist of a numerator and a denominator and no whole numbers. Converting 5 wholes into fourths would mean 5 times 4 which is 20. Therefore 5 converted into 1/4 ‘s is 20 1/4’s. This combined with the other 1/4 in the fraction 5 1/4 makes the improper fraction 21/4.
When you divide fractions you switch the numerator and denominator of the fraction on one side (usually the right side although it doesn’t matter as long as you only switch one fraction of the two) and multiply. 15 times now 4/21 is 60/21.
To simplify this you can divide the numerator and denominator by a common factor. We can start with 3, simplifying the fraction to 20/7. Now as you may notice in the answer choices they are all mixed numbers, consisting of a whole number as well as the numerator and denominator. 20/7 as a mixed number is 2 6/7 as you can have 2 times 7 (14) and then have 6 left so you have 2 wholes and 6/7 away from another whole. This makes C the answer