1. The problem asks for an expression for the area of a trapezium with parallel sides labeled $3x - 3$ and $5x$, and height $3x$. 2. Recall the formula for the area of a trapezium: $$\text{Area} = \frac{(\text{sum of parallel sides}) \times \text{height}}{2}$$ 3. Substitute the given expressions into the formula: $$\text{Area} = \frac{(3x - 3 + 5x) \times 3x}{2}$$ 4. Simplify inside the parentheses: $$3x - 3 + 5x = 8x - 3$$ 5. Now the area expression is: $$\text{Area} = \frac{(8x - 3) \times 3x}{2}$$ 6. Multiply the terms in the numerator: $$(8x - 3) \times 3x = 24x^2 - 9x$$ 7. So the area is: $$\text{Area} = \frac{24x^2 - 9x}{2}$$ 8. This is the simplified expression for the area of the trapezium in terms of $x$. **Final answer:** $$\boxed{\frac{24x^2 - 9x}{2}}$$