The correct answer to this question is 13. Though the problem says HCF, I believe it means to say GCF, which stands for the most significant common factor. Used in math, GCF is the highest number, which can be divided into two or more numbers.
To answer this, we should first find the factors of 39 and 52 individually. The elements of 39 are 1, 3, 13, and 39. The elements of 52 are 1, 2, 4, 13, 26, 52. Looking at those two lists, we find what they have in common. They both have 1 and 13 in stock. The higher number between those two is 13, which is our GCF.