Talia did 62 - 20 = 42, instead of 62 - 17
Since she subtracted 20 instead of 17, that means she over subtracted by 3. To get the correct answer she has to add back 3 to her initial answer.
Since she over subtracted.
So she has to add 3, that is 42 + 3 = 45
Hope this explains it.
