The diagram given below shows two sticks $-$ one $BLACK$ and the other $WHITE$. Based on the measurements shown,what is the length of the white stick? (in $cm$)

For a pair of equations $7x - 13y = 1$ and $13x - 7y = 19$,find the value of $x - y$.

The sum of two positive numbers is $25$. Five times the smaller number is $5$ more than three times the larger number. Represent this as a pair of linear equations in two variables.

Determine,graphically,the vertices of the triangle formed by the lines $y=x$,$3y=x$,and $x+y=8$.

$A$ boat goes $32 \, km$ upstream and $36 \, km$ downstream in $7$ hours. In $9$ hours,it can go $40 \, km$ upstream and $48 \, km$ downstream. Determine the speed of the stream and that of the boat in still water. (Speed of boat in still water is more than the speed of the stream of river.)

Comparing the equation $x=4$ with the standard form $ax+by+c=0$,we get $b=\ldots \ldots \ldots$