How many neutrons does element x have if its atomic number is 36 and its mass number is 70?

If the atomic number equals the number of protons there is in an element then the mass equals the number of neutrons and protons added together thus we have 36 protons plus x amount of neutrons = a mass of 70.  

36+x=70

x=34 neutrons

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.