a) $$8000 \cdot 60000 = 480000000$$
б) $$1700 \cdot 800000 = 1360000000$$
в) $$250000 \cdot 600 \cdot 40 = (250000 \cdot 40) \cdot 600 = 10000000 \cdot 600 = 6000000000$$
г) $$19000 \cdot 20000 \cdot 50 = (20000 \cdot 50) \cdot 19000 = 1000000 \cdot 19000 = 19000000000$$
Ответ: a) 480000000; б) 1360000000; в) 6000000000; г) 19000000000