​​how long ago did the poets mother take her dying breath from the chapter a photograph

Ans. We can say this becuz of the following lines"Now she's has been dead nearly as many years as that girl lived." From this we understand that the women has been dead for as many years as that girl in the photograph was old when picture was clicked. In the initially part of poem we come to know that the girl in picture was 12 yrs of age. Hence we can say that the women was dead for 12yrs.

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