The energy released in the following reaction.

${\mathrm{He}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{He}$

If ionization energy of H is -13.6 eV and He is -24.6 eV.

Number of electrons present in H is one and there is zero electrons in H⁺. Energy required for the formation of H from H⁺ is -13.6 eV.

Number of electrons present in He is 2. For conversion of He²⁺ to He, four electrons are needed. 

According to Bohr's model, energy released from an atom is calculated as:

$E=-13.6\frac{z^2}{n^2}$

Here, z is the atomic number and n is the number of electrons.

The energy required for the conversion of He²⁺ to He is done by adding energies for the conversion of He²⁺ to He⁺ and He⁺ to He.

$Energy=E_{{\mathrm{He}}^{2+}\to {\mathrm{He}}^{+}}+E_{{\mathrm{He}}^{+}\to \mathrm{He}}\cdots \left(1\right)$

Energy needed for conversion of He²⁺ to He⁺ is calculated as:

$\begin{array}{ccc}{E}_{{\mathrm{He}}^{2+}\to {\mathrm{He}}^{+}}& =& -13.6\frac{{\left(2\right)}^2}{{\left(1\right)}^2} \mathrm{eV}\\ & =& -54.4 \mathrm{eV}\end{array}$

Energy for the conversion of He⁺ to He is given as -24.6 eV.

Substitute both energy values in equation (1).

$\begin{array}{ccc}\mathrm{Energy}& =& -24.6 \mathrm{eV}+(-54.4 \mathrm{eV})\\ & =& -79 \mathrm{eV}\end{array}$