The following table shows the number of fire hydrants in each neighborhood overseen by Fire District $9$.
Neighborhood | Number of fire hydrants
- | :-:
Clearwater Estates | $17$
Shamrock Oak | $15$
Hidden Village | $21$
Tower Terrace | $12$
Prairie Pass | $\large?$
**If the mean of the data set is $15$ fire hydrants, find the number of fire hydrants in Prairie Pass.**
$\qquad$[[☃ numeric-input 1]] fire hydrants