The transformation occurring in Duma's method is given below :
$\mathrm{C}_{2} \mathrm{H}_{7} \mathrm{~N}+\left(2 \mathrm{x}+\frac{\mathrm{y}}{2}\right) \mathrm{CuO} \rightarrow \mathrm{xCO}_{2}+\frac{y}{2} \mathrm{H}_{2} \mathrm{O}+\frac{\mathrm{z}}{2} \mathrm{~N}_{2}+\left(2 \mathrm{x}+\frac{\mathrm{y}}{2}\right) \mathrm{Cu}$
The value of $y$ is (Integer answer)
$\mathrm{C}_{2} \mathrm{H}_{7} \mathrm{~N}+\left(2 \mathrm{x}+\frac{\mathrm{y}}{2}\right) \mathrm{CuO} \rightarrow \mathrm{x} \mathrm{CO}_{2}+\frac{\mathrm{y}}{2} \mathrm{H}_{2} \mathrm{O}+\frac{\mathrm{z}}{2} \mathrm{~N}_{2}+\left(2 \mathrm{x}+\frac{\mathrm{y}}{2}\right) \mathrm{Cu}$
On balancing
$\mathrm{C}_{2} \mathrm{H}_{7} \mathrm{~N}+\frac{15}{2} \mathrm{CuO} \rightarrow 2 \mathrm{CO}_{2}+\frac{7}{2} \mathrm{H}_{2} \mathrm{O}+\frac{1}{2} \mathrm{~N}_{2}+\frac{15}{2} \mathrm{Cu}$
On comparing
$y=7$