7.1. The sides of a rectangle are in the ratio $3: 4$, and its area is numerically equal to its perimeter. Find the sides of the rectangle.
Answer: 7/2, 14/3. Solution. Let $x$ and $y$ be the sides of the rectangle, then the equalities $4 x=3 y$ and $x y=2(x+y)$ hold. Expressing $x$ from the first equality and substituting it into the second, we get (after dividing by $y \neq 0$) $x=7 / 2, \quad y=14 / 3$.