Answer
see an explanation
Work Step by Step
$A(t)=A_{0}e^{kt},$
$A_{0}$ is the Initial amount.
$k$ is negative number.
a. From the formula $A(t)=A_{0}e^{-0.087t},$ Whereas $A_0$ is the Initial amount and $A(t)$ is the amount remaining after $t$ days. The decay rate is, $k=-0.087.$
b.$A(9)=100e^{-0.087\times 9}=45.7,$
c.
$A(t)=100e^{-0.087t}=70,$
$e^{-0.087t}=0.7,$
$-0.087t=\ln{0.7},$
$t=4.1,$
d.
$A(t)=100e^{-0.087t}=50,$
$e^{-0.087t}=0.5,$
$-0.087t=\ln{0.5},$
$t=7.97$
