There are two types of annual plan:
- Annual plan, paid in full upfront
- Annual plan, paid month by month
Looks like you have the 2nd option for Photoshop Single App and you're cancelling at month 3.
So your early termination fee is ($158*9)/2 = $711.
There are much cheaper ways of getting Photoshop, if that's all you want.
Have a look at the Photography Plan for HK$68/month which gives you both Photoshop and Lightroom..