Given :7872 ÷ 305.
Because it's estimation. So, we need to estimate the number 7872 to 8000.
In order to divide 8000 by a number we need to estimate 305 to the 400. Because 400 is exact divisor of 8000.
If we divide 8000 by 400 we get 20.
And it's obviously less then 60000 ÷ 300= = 200.
20 < 200.
Therefore, Harrison is absolutely correct.