1. **Stating the problem:** We are given a survey of 60 pupils about their favorite drinks: cola, milk, and water. We know the number of boys and girls who prefer each drink and need to find how many pupils in total prefer cola. 2. **Given data:** - Total pupils: $60$ - Boys: $32$ - Boys who like cola: $12$ - Boys who like water: $4$ - Girls who like water: $9$ - Pupils who like milk: $21$ 3. **Step 1: Find the number of girls.** Since total pupils are $60$ and boys are $32$, girls are: $$60 - 32 = 28$$ 4. **Step 2: Find the total number of pupils who like water.** Water lovers = boys who like water + girls who like water: $$4 + 9 = 13$$ 5. **Step 3: Use the total pupils and the number who like milk and water to find those who like cola.** Total pupils = pupils who like cola + pupils who like milk + pupils who like water Let $x$ be the number of pupils who like cola: $$x + 21 + 13 = 60$$ 6. **Step 4: Solve for $x$.** $$x = 60 - 21 - 13 = 26$$ 7. **Answer:** $$\boxed{26}$$ pupils said that cola was their favourite drink.