$40 ... 160 minutes
$1 ... x minutes = ?
If you would like to know how many minutes of talk time does Tiffany get per dollar, you can calculate this using the following steps:
40 * x = 1 * 160
40 * x = 160 /40
x = 160 / 40
x = 4 minutes
Result: Tiffany gets 4 minutes of talk time per dollar.