In a two-digit number,the digit at unit's place is $x$ and the digit at ten's place is $y$. The number obtained by interchanging the digits is ...........

The solution set of a pair of equations $5x - 5y = -5$ and $\frac{3x}{2} - \frac{3y}{2} + \frac{3}{2} = 0$ is.........

$A$ railway half ticket costs half the full fare,but the reservation charges are the same on a half ticket as on a full ticket. One reserved first class ticket from station $A$ to $B$ costs $Rs. 2530$. Also,one reserved first class ticket and one reserved first class half ticket from $A$ to $B$ costs $Rs. 3810$. Find the full first class fare from station $A$ to $B$,and also the reservation charges for a ticket (in $Rs.$).

The pair of equations $5x - y = 9$ and $10x - 18 = 2y$ is $\ldots \ldots \ldots \ldots$

If $\frac{3}{x}-\frac{2}{y}=5$ and $\frac{4}{x}-\frac{5}{y}=2,$ then the value of $\frac{1}{x}-\frac{1}{y}$ is ............ $(x, y \neq 0)$

If the following pair of equations has infinite solutions,then find the value of $k$:
$5x + 2y = k$
$10x + 4y = 3$