Ответ: $$15 \cdot 10 + (30 - 20) \cdot 5 =$$ $$= 150 + 10 \cdot 5 =$$ $$= 150 + 50 = 200$$ $$15 \cdot 10 + 30 - 20 \cdot 5 =$$ $$= 150 + 30 - 100 =$$ $$= 180 - 100 = 80$$