Divide the remaining miles of the trip by the miles per gallon her car gets. 220 miles / 20 miles/gallon = <<220/20=11>>11 gallons
Subtract the gallons used for the trip from the size of her gas tank. 16 gallons - 11 gallons = <<16-11=5>>5 gallons
Multiply the remaining number of gallons by the car's gas mileage. 5 gallons x 20 miles/gallon = <<5*20=100>>100 miles
#### 100