e^(-t)=0.01 t=
e^(-t)=0.01 take the ln of both sides
ln e^(-t)= ln(0.01) and by a log property, we can write
(-t) ln e = ln (0.01) and ln e = 1, so we can forget this term
-t = ln (0.01) multiply both sides by -1
t = -ln(0.01) = about 4.605
