Question

is the atomic mass of hydrogen
is the atomic mass of helium

Answer 1

The mass of an atom is measured in terms of atomic mass unit (1 amu).
1 amu is defined as the mass equal to one-twelfth (1/12th) of the mass of one carbon-12 atom.
The mass of C-12 atom is taken as the standard to measure the mass of other atoms.
Thus, the atomic mass of hydrogen is 1 amu and that of helium is 4 amu.