A radioactive substance decays exponentially, as shown in the table below. The amount of substance is measured in grams. At this rate, on which day would the amount of the substance first be less than or equal to $1.25\times 10^6$ grams?

Day	Amount of substance (grams)
1	$8.0\times 10^7$
2	$4.0\times 10^7$
3	$2.0\times 10^7$