A father is now three times as old as his son. Seven years back, he was four times as old as his son. The age of the son (in years) is  Choose the correct choice from the following.
A) 12	B) 15	C) 18	D) 20	E) 21
If father's age is F and son's age is S, then   F=3S   and   F-7 = 4*(S-7)   3S-7 =4S-28   S=21   F=63 years   ANSW21R:21
<result>E</result>
A father is now three times as old as his son. Seven years back, he was four times as old as his son. The age of the son (in years) is