1B. Dime has twice as many brothers as sisters, and his sister Maria has five times as many brothers as sisters. How many brothers and how many sisters are there in this family?
Solution. Let there be $x$ male children and $y$ female children in the family. The number of sisters Dime has is $y$, and the number of brothers is $x-1$. From the condition of the problem, we have that $x-1=2 y$. The number of sisters Maria has is $y-1$, and the number of brothers is $x$. Then, we have that $x=5(y-1)$.

By solving the system of equations $x-1=2 y$ and $x=5(y-1)$, we get that $x=5$ and $y=2$.

2AB. The proper fraction $\frac{a}{b}$ can be represented in the form $\frac{6}{n}-\frac{9}{n^{2}}$, where $n$ is a natural number. Determine the value of $a$, if $b-a=961$.