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A father is 36 yrs old and his son is a quarter of his;
so, the son's age is 1/4 of 36 = 9.
let y = number of years
36 + y = 2 • ( 9 + y ) + 7
36 + y = 18 + 2y + 7
36 + y = 25 + 2y
............................subtract y & 25 from both sides of the equation;
36 + y - y - 25 = 25 + 2y - y...
