Answer
8 years
Work Step by Step
We are given:
$INT=FV-PV=640$ for $PV=1000$ at $r=0.008,$
we don't know the time of maturing, $t=?$
Simple interest formula:
$FV=PV(1+rt),\qquad $we solve for t.
$FV=PV+PVrt\qquad /-PV$
$FV-PV=PVrt\qquad/\div(PV\cdot r)$
$t=\displaystyle \frac{FV-PV}{PV\cdot t}=\frac{640}{1000\cdot 0.08}=8$
The loan matures in $8$ years
