Question 996285
The sum of the present age of a father and his daughter is 42 years.
f + d = 42
f = 42 - d
7 years later, the father will be three times older than the daughter.
f + 7 = 3(d + 7)
f + 7 = 3d + 21
f = 3d + 21 - 7
f = 3d + 14
Replace f with (42-d)
42 - d = 3d + 14
42 - 14 = 3d + d
28 = 4d
d = 28/4
d = 7 yrs is the present age of the daughter
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You can check the solution yourself, find f and use these ages in the 2nd statment