7.3. If the first digit of a two-digit natural number $N$ is multiplied by 4, and the second digit is multiplied by 2, then the sum of the numbers obtained after the multiplication will give $\frac{N}{2}$. Find $N$ (list all solutions).
Answer: three solutions: $N=32 ; 64 ; 96$. Solution. Let $x$ be the first digit, $y$ be the second digit of the number $N$. Then the condition of the problem can be written as $4 x+2 y=\frac{10 x+y}{2} \Leftrightarrow 2 x=3 y$. Therefore, the digit $x$ is divisible by 3 and $x \neq 0$ (since $x$ is the first digit). From this, we get three solutions: $x=3$, or $x=6$, or $x=9$, and accordingly $y=2$, or $y=4$, or $y=6$.