All elements have a δhf of 27314.1840 kj/mole at standard temperature and pressure.

All elements have a ΔHf of 0 (zero) at standard temperature and pressure.

Standard ΔHf of formation is the standard enthalpy (heat) of formation of the compound. It is defined as the change of enthalpy when one mol of compound is formed  in its standard state from the elements in their standard state.

Then, as the elements are already in their standard state, there is not any change and the standard enthalpy of an element in its standard state is, by definition, zero.

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

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