What will the area of the wound be on day 8
on what day will the area of the wound be less than one square millimeter

So hmmm if we notice, we have 70, 49, 34.3 and so on

so... from 70 to 49, is 21 less

now, what is 21 of 70? well 

so is 30%, that means 49 is the 70%

ok, now, how much is the 70% of 49? well , simply (70/100)*49, which gives us 34.3

how much is the 70% of 34.3, well 0.7*34.3 or 24.01 and so on

so every day, the wound is shrinking by 30%

thus   r=30% or 30/100 which is r = 0.30