1. The problem states the formula $C = kab$, where $C$ is a variable dependent on $k$, $a$, and $b$. 2. This formula represents a direct variation where $C$ varies directly as the product of $a$ and $b$ multiplied by a constant $k$. 3. To use this formula, you need to know the values of $k$, $a$, and $b$ to find $C$. 4. For example, if $k=2$, $a=3$, and $b=4$, then: $$C = 2 \times 3 \times 4 = 24$$ 5. This means $C$ equals 24 when $k=2$, $a=3$, and $b=4$. 6. The key rule is that $k$ is a constant multiplier, and $a$ and $b$ are variables that affect $C$ multiplicatively.