The discount for an iPhone 12 is $800 x 15/100 = $<<800*15/100=120>>120.
So, the iPhone will now cost $800 - $120 = $<<800-120=680>>680.
The discount for an iWatch is $300 x 10/100 = $<<300*10/100=30>>30.
So, the iWatch will now cost $300 - $30 = $<<300-30=270>>270.
The total cost of the iPhone and iWatch is $680 + $270 = $<<680+270=950>>950.
The cashback will be $950 x 2/100 = $<<950*2/100=19>>19.
Thus, Dexter will only pay $950 - $19 = $<<950-19=931>>931.
#### 931