Question

Nitrogen has an atomic mass of about 14 amu and an atomic number of 7. How many neutrons does nitrogen have?

Answer 1

So 14-7=7. There are 7 neutrons.

Answer 2

So the atomic number of an element tells the number of proton in the element.
The atomic mass is the sum of the number of protons and neutrons.

From this we can draw up and equation:
           Atomic Mass =  (# of protons)  +  (# of neutrons)
     
    ⇒  # of neutrons = Atomic Mass - Atomic Number
                               = 14  -  7
                               =  7

Therefore nitrogen has SEVEN neutrons.