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Answer:
3.8 miles
Explanation:
Lillian wants her mileage total to be ...
12 +3x = 23.4 . . . . an equation that can be used to find x
4 + x = 7.8 . . . divide by 3
x = 3.8 . . . . . . subtract 4
Lillian would have to ride an average of 3.8 miles each day to reach her goal.