Their car broke down 120 miles from home.
Since both distances to and fro are the same, we have that
30t = d (1) and 20t' = d (2)
30t = 20t' (3)
Also, since they wer gone for 10 hours, we have that t + t' = 10 (4)
So, t' = 10 - t
Substituting t' into (3), we have
30t = 20(10 - t)
30t = 200 - 20t
30t + 20t = 200
50t = 200
t = 200/50
t = 4 hours.
Substituting t into (1), we have
d = 30t
= 30 × 4
= 120 miles
So, their car broke down 120 miles from home.
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