I believe the equation would look like 1/3z+3=13.
When dealing with these types of problems you need to understand and recognize certain words. For example, more than always means addition, whatever number will be added to another term. With fractions, when the question says “1/5 the number” or in this case “1/3 the number” it will mean multiplication. So we could always put together 1/3z+3. Lastly, the questions states that 13 protons IS 3 more than 1/3 the number, in meaning our expression will equal to 13 which creates the equation 1/3z+3=13.
This can also be proven correct because this questions actually follows how many protons each atom have, aluminum has 13 while zinc has 30.