Hey there!
This atom has 10 protons.
If this atom has an atomic mass of 22, that means the sum of protons and neutrons is 22.
p + n = 22
p = 10
Which makes this true:
10 + n = 22
Subtract 10 from each side to solve for n, the number of neutrons.
n = 12
An atom that has the atomic number of 10 and an atomic mass of 22 has 12 neutrons.
Hope this helps!