Answer:
7amu
Step-by-step explanation:
Atoms are composed of three particles. The proton, neutron, and electron.
The mass of the atom in amu is just the number of protons and neutrons in the nucleolus since they both have a mass of about 1 amu. Electrons are not counted since they have an incredibly small mass that ultimately does not matter.
This atom has 3 protons (positively charged particle) and 4 neutrons (particle with no charge) which together gives a mass of 7 amu.