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Let x be the Sarah age. Then the Sheila age is x-7 years.
Sarah's age 6 years from now is (x+6) years;
Sheila's age 7 years ago is/was ((x-7)-7) = x-14 years.
So, the number 69 is the product of factors (x+6) and x-14 with the difference between them of 20.
There is only one such a pair in positive integer numbers: it is (23,3).
So, x+6 = 23, which means that Sarah is 17 years old, while Sheila is 17-7 = 10 years old. ANSWER
Solved.