Which formula is used in the Kjeldahl method for the estimation of nitrogen?

The transformation occurring in Dumas's method is given below:
$C_{2}H_{7}N + (2x + \frac{y}{2})CuO \rightarrow xCO_{2} + \frac{y}{2}H_{2}O + \frac{z}{2}N_{2} + (2x + \frac{y}{2})Cu$
The value of $y$ is ...... .(Integer answer)

On complete combustion,$0.246 \ g$ of an organic compound gave $0.198 \ g$ of carbon dioxide and $0.1014 \ g$ of water. Determine the percentage composition of carbon and hydrogen in the compound.

In $Duma's$ method for estimation of nitrogen,$0.25 \ g$ of an organic compound gave $40 \ mL$ of nitrogen collected at $300 \ K$ temperature and $725 \ mm$ pressure. If the aqueous tension at $300 \ K$ is $25 \ mm$,the percentage of nitrogen in the compound is:

$2.18 \ g$ of an organic compound containing sulphur produces $0.12 \ g$ of $BaSO_4$. The percentage of sulphur in the compound is?

Why is a solution of potassium hydroxide used to absorb carbon dioxide evolved during the estimation of carbon present in an organic compound?