Question 1139426
{{{90=100e^(-4k)}}}

{{{0.9=e^(-4k)}}}

{{{ln(0.9)=-4k}}}

{{{k=-ln(0.9)/4}}}

{{{k=0.02634}}}

MODEL:  {{{d=De^(-0.02634t)}}}  or {{{d=100e^(-0.02634t)}}}.