1. **State the problem:** We need to find the total cost to buy carpet to cover the floor of a square-shaped room with side length 4 metres, where the carpet costs 99 per square metre. 2. **Formula for area of a square:** The area $A$ of a square with side length $s$ is given by: $$A = s^2$$ 3. **Calculate the area:** Substitute $s = 4$ metres: $$A = 4^2 = 16 \text{ square metres}$$ 4. **Calculate the total cost:** Multiply the area by the cost per square metre: $$\text{Cost} = 16 \times 99$$ 5. **Perform the multiplication:** $$\text{Cost} = 1584$$ 6. **Final answer:** The total cost to buy enough carpet is 1584.