Question 1115087
maybe this kind of model?
{{{y=55e^(-kt)}}}


{{{55=55e^(-k*0)}}}


{{{30=55*e^(-12k)}}}

{{{e^(-12k)=30/55=3*5/(5*11)}}}

{{{e^(-12k)=3/11}}}

{{{ln(e^(-12k))=ln(3/11)}}}

{{{-12k=ln(3/11)}}}

{{{k=-ln(3/11)/12}}}

{{{highlight(k=0.10827)}}}


{{{highlight(y=55e^(-0.10827t))}}}, for t years since 1985