1) 304 would round to 300, 9.96 would round to 10, and 0.51 would round to 0.5, so your final expression would be (300 × 10)/0.5. 300 × 10 = 3000, and 3000 ÷ 0.5 = 6000, which is your answer.
2) 6.7 would round to 7, 192 would round to 200, and 0.051 would round to 0.05. (7 × 200)/0.05. 7 × 200 = 1400, and 1400 ÷ 0.05 = 28,000, which is your answer.
I hope this helps!