A scientist measures the initial amount of carbon-141414 in a substance to be 252525 grams. The relationship between aaa, the amount of carbon-141414 remaining in that substance, in grams, and ttt, the elapsed time, in years, since the initial measurement is modeled by the following equation. A=25e^{-0. 00012t}a=25e −0. 00012t a, equals, 25, e, start superscript, minus, 0, point, 00012, t, end superscript in how many years will the substance contain exactly 202020 grams(\text{g})(g)left parenthesis, start text, g, end text, right parenthesis of carbon-141414? give an exact answer expressed as a natural logarithm.