A cellbphone company charges $10 per month for up to 500 text messages and $0.15 for each additional text message. Stanley was charged $14.50 last month for text messages.

10 + .15(n-500) = 14.50

X text messages.

10 + 0.15x = 14.50.
X = 30.

To find out how many additional text messages Stanley sent last month, we need to calculate the difference between what he was charged and the cost for the first 500 messages.

First, let's calculate the cost for the first 500 text messages:
500 text messages at $0.15 per text message = $75

Since Stanley was charged a total of $14.50, we subtract the cost for the first 500 messages:
$14.50 - $10.00 = $4.50

This $4.50 represents the additional cost for the extra text messages.

To find out how many additional text messages were sent, we divide the additional cost by the cost per text message:
$4.50 / $0.15 = 30

Therefore, Stanley sent 30 additional text messages last month.