Respuesta :
an atomic mass stands for how many protons an element has and an atomic number takes the number of protons plus the number or neutrons.
that being stated you would subtract the atomic number from the atomic mass.
Making your answer A:4
Easy, your answer is A:4.
This is because to find the neutrons in an atom,
all you have to do is subtract the atomic number by the mass number.
I hope that answered your question :)