Presuming both Sally and her mother were born on the same date (n/m) and this calculation was performed on their birthday.
80-54=26
Sally's mother is 26 years older than her.
--------------
0:26
1:27
2:28
3:29
4:30
5:31
6:32
7:33
8:34
9:35
10:36
11:37
12:38
13:39 <----- When Sally's mother was 3 times her age, as 13*3=39
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When was Sally's mother 39?
41 years ago, as 80-39=41.
