First,
the age of the son: s
the age of the father is 2 less than 7 times the age of his son: 7s - 2
In 3 years, the sum of their ages will be 52,
In 3 years, the age of the sun will increase 3, so s+3. Also, the age of his father also increase 3, (7s - 2) + 3
(s+3) + [(7s-2) + 3] = 52 is the equation.