$83,000 / 20 = $4150 per year
$4150/12= $345.83 per month
and it is $345,83/30=$11.52 per day
if she reduced $7.63 his monthly payment, she paid $345,83-$7.63=$338.2
so she must pay the remaining $7.63
1day-------->$11.52
?<-------------$7.63
7.63/11.52= 0.6 day = 6hours
minimum amount of time is 6 hours