17. The father’s age is six times his son’s age. Four years hence, the age of the father will be four times his son’s age. The present ages, in years, of the son and the father are, respectively

(a) 4 and 24 
(b) 5 and 30
(c) 6 and 36 
(d) 3 and 24
Answer: (c) 6 and 36
Explanation:
Let x years be the present age of father and y years be the present age of son. 
According to the given,
(x + 4) = 4(y + 4) 
x + 4 = 4y + 16 
x- 4y + 4 – 16 = 0
x – 4y – 12 = 0….(i) 
Also, x = 6y….(ii) 
From (i) and (ii),
6y – 4y – 12 = 0 
2y = 12 
y = 6
Substituting y = 6 in (ii),
x = 6(6) = 36