Answer
Get values for balance, purchases, payment
Set the value of unpaid to balance + purchases - payment
If unpaid < 100 then
$\ \ \ \ \ \ $ Set the value of interest to unpaid $\times$ 0.08
Else
$\ \ \ \ \ \ $ If unpaid $\leq$ 500 then
$\ \ \ \ \ \ $ $\ \ \ \ \ \ $ Set the value of interest to unpaid $\times$ 0.12
$\ \ \ \ \ \ $ Else
$\ \ \ \ \ \ $ Set the value of interest to unpaid $\times$ 0.16
Set the value of newbalance to unpaid + interest
Print the value of newbalance
Stop
Work Step by Step
Get values for balance, purchases, payment
Set the value of unpaid to balance + purchases - payment
If unpaid < 100 then
$\ \ \ \ \ \ $ Set the value of interest to unpaid $\times$ 0.08
Else
$\ \ \ \ \ \ $ If unpaid $\leq$ 500 then
$\ \ \ \ \ \ $ $\ \ \ \ \ \ $ Set the value of interest to unpaid $\times$ 0.12
$\ \ \ \ \ \ $ Else
$\ \ \ \ \ \ $ Set the value of interest to unpaid $\times$ 0.16
Set the value of newbalance to unpaid + interest
Print the value of newbalance
Stop