1. **State the problem:** We need to find the area of a trapezium with bases $a=8$ cm, $b=9$ cm, and height $h=6$ cm. 2. **Formula:** The area $A$ of a trapezium is given by the formula: $$A = \frac{1}{2} (a + b) h$$ This formula calculates the average length of the two parallel sides multiplied by the height. 3. **Substitute the values:** $$A = \frac{1}{2} (8 + 9) \times 6$$ 4. **Simplify inside the parentheses:** $$8 + 9 = 17$$ So, $$A = \frac{1}{2} \times 17 \times 6$$ 5. **Multiply:** $$\frac{1}{2} \times 17 = 8.5$$ Then, $$8.5 \times 6 = 51$$ 6. **Final answer:** The area of the trapezium is **51 cm²**.