A father said to his son, "I was as old as you are at the present at the time of your birth". If the father's age is 42 years now, the son's age 4 years back was:	Choose the correct choice
A) 12 years.	B) 14 years.	C) 17 years.	D) 16 years.	E) 19 years.
Let the son's present age be x years. Then, (42 - x) = x   2x = 42.   x = 21   Son's age 5 years back (21- 4)= 
<gadget id="calculator">(21- 4)</gadget>
<output>17</output>
17 years.   ANSWER :17 years.
<result>C</result>
A father said to his son, "I was as old as you are at the present at the time of your birth". If the father's age is 42 years now, the son's age 4 years back was: