Answer: 15 miles 
Explanation:
Given : Distance walked by Elena before = 12 miles 
After that she walked = 


Total distance she waled = (Distance walked by Elena before) + (After that she walked)
i.e. Total distance she waled = 12 miles+ 3 miles 
i.e.T otal distance she waled = 15 miles
Hence, she walked 15 miles all together.