The diagram shows an object with weight $W$ and an object with weight $Z$ in balance on a uniform metre rule. Which equation linking $W$, $Z$, $a$ and $b$ is correct?
- A$\frac{W}{a} = \frac{Z}{b}$
- B$W \times Z = a \times b$
- C$W \times a = Z \times b$
- D$W \times (a + b) = Z$