Answer:
$72
Explanation:
For the first month, they got a 25% discount, aka $120 off. Now that it's changed to 40%, you need to find how much 40% of $480 is.
480 x .4 = 192
40% of $480 is $192. The next step is to find the difference between $192 and $120.
192 - 120 = 72
Therefore, you need to give them of refund of $72.