Answer:
21 miles
Explanation:
Big Bird's nest is halfway between Bert's place and Ernie's place, so the distance from the nest to either apartment is the same. Equating those distances, we have ...
... 5x +4 = 15x -30
... 34 = 10x . . . . . . add 30-5x
... 3.4 = x . . . . . . . .divide by 10
The value of x is not the distance. The distance is given by either of the two expressions
Using the first of these, the distance from either apartment to Big Bird's nest is ...
... 5·3.4 +4 = 17 +4 = 21 . . . . miles
Of course, using the second gives the same answer:
... 15·3.4 -30 = 51 -30 = 21