The distance of Jane's house is 3.12 miles.
The time spent by Jane during the journey is calculated as follows;
from 12:30 PM to 3:30 PM = 3 hours
time  spent by Jane biking  = 3 hours - 90 minutes
                       = 3 hours - 1.5 hours
                       = 1.5 hours
let the time taken during her first motion before coming back = t
12t = 2.5(1.5 - t)
12t = 3.75 - 2.5t
14.5t = 3.75
t = 3.75/14.5
t = 0.26 hr
distance = 12 miles/hr x 0.26 hr
distance = 3.12 miles
Thus, the distance of Jane's house is 3.12 miles.
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