$\therefore $ $\Delta Q = n{C_P}\Delta T$ and $\Delta U = n{C_V}\Delta T$

Also $\Delta W = \Delta Q - \Delta U = \mu \,({C_P} - {C_V})\,\Delta T$

$\therefore \,\,\,\,\,\,\frac{{\Delta Q}}{{\Delta W}} = \frac{{n{C_P}\Delta T}}{{n\,({C_P} - {C_V})\,\Delta T}}$$ = \frac{{{C_P}}}{{{C_P} - {C_V}}} = \frac{1}{{1 - \frac{{{C_V}}}{{{C_P}}}}}$

$\frac{{{C_V}}}{{{C_P}}} = \frac{3}{5}$ for helium gas. Hence $\frac{{\Delta Q}}{{\Delta W}} = \frac{1}{{1 - 3/5}} = \frac{5}{2}$