The 10 power root of (1-x) = 1/2,

( 1-x)=0.93303

x=0.066967

Answer the first question: the percentage of the area cut down every year is 6.6967%.

The answer to the second question: It is known that the remaining forest area is 35.355% of the original, so the n power of a (1-x) =a×35.355%.

N= 15, the forest was cut down 15 years.

Answer the third question: if the forest area should be kept at least 25% of the original area, it can be cut down for 20 years, because it has been cut down for 15 years, and it can be cut down for up to 5 years in the future.