* Protons and Neutrons: The vast majority of an atom's mass comes from its protons and neutrons. These particles each have a mass of approximately 1 atomic mass unit (amu).

* Electrons: Electrons are much smaller and have a negligible mass compared to protons and neutrons.

Calculation:

1. Protons: 34 protons * 1 amu/proton = 34 amu

2. Neutrons: 45 neutrons * 1 amu/neutron = 45 amu

3. Total Mass: 34 amu + 45 amu = 79 amu

Therefore, the mass of an atom with 34 protons, 34 electrons, and 45 neutrons is approximately 79 atomic mass units (amu).