1. Let's state the problem: We know the lighthouse is 30 metres tall. 2. To find the height of the cliff, we typically need additional information such as total height or a relationship involving the lighthouse and the cliff. 3. Since no further data is provided, we assume the total height (cliff plus lighthouse) or a ratio should be given to find the cliff height. 4. Please provide more details or the total height or another relevant measurement. 5. Without more info, we cannot calculate the cliff height accurately.