The discount for the Delta flight would come to $850 * 0.20 = $<<850*0.20=170>>170.
The final price of the Delta flight would come to $850 - $170 = $<<850-170=680>>680.
The discount of the United flight would come to $1100 * 0.30 = $<<1100*0.30=330>>330.
The final price of the United flight would come to $1100 - $330 = $<<1100-330=770>>770.
The Delta flight would be cheaper than the United flight by $770 - $680 = $<<770-680=90>>90.
#### 90