All atoms of the same element

Atoms of the same element can have different numbers of neutrons, however. Atoms of the same element with different numbers of neutrons are called isotopes. Most naturally occurring elements exist as isotopes.

Explanation:

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer