1. **State the problem:** We need to find the percentage reduction in the cost of a t-shirt when it is reduced from £18 to £12.60. 2. **Calculate the amount of reduction:** The reduction amount is the original price minus the new price. $$18 - 12.60 = 5.40$$ 3. **Calculate the percentage reduction:** Percentage reduction is given by the formula $$\text{Percentage reduction} = \left(\frac{\text{Reduction amount}}{\text{Original price}}\right) \times 100$$ Substitute the values: $$\left(\frac{5.40}{18}\right) \times 100 = 0.3 \times 100 = 30\%$$ 4. **Answer:** The percentage reduction in the cost of the t-shirt is **30%**.