To understand isotope notation and how to use it to determine the number of protons

To understand isotope notation and how to use it to determine the number of protons and neutrons and the mass number for atoms. Atoms with the same number of protons but different numbers of neutrons are called isotopes. Some elements only have one naturally occurring isotope, while others such as carbon have two or more. In a naturally occurring sample, isotopes of each element are present in a certain percentage amount called the percent natural abundance.
The mass number of an isotope is the sum of the number of protons and the number of neutrons for a particular isotope and is symbolized by A.
A=number of protons+number of neutrons
There are several different types of isotope notation. For example, a carbon isotope that has an atomic number of 6 and a mass number of 13 could be symbolized in any of the following ways: 13 6C, carbon-13, or C-13.
Write the appropriate symbol for an isotope of potassium-39 corresponding to the isotope notation AZX.
Express your answer as a chemical symbol using isotope notation.