1. The problem is to understand the concept of a formula and see an example. 2. A formula is a mathematical rule or relationship expressed using symbols and variables. 3. For example, the formula for the area $A$ of a rectangle is: $$A = l \times w$$ where $l$ is the length and $w$ is the width. 4. To use this formula, you substitute the values of length and width into the formula and multiply them. 5. For example, if $l = 5$ and $w = 3$, then: $$A = 5 \times 3 = 15$$ 6. So, the area of the rectangle is 15 square units. This shows how a formula provides a way to calculate a quantity based on given values.