Let us take the son's and father's present age as 'x' and 'y'.

It is given that, $x + y = 70$ --------> 1

After $10$ years, son's age will be $(x + 10)$ and father's age will be

$( y + 10)$. It is also given that,

$x + 10 = ( y + 10 )/2$ ----------> 2 

From equation 1 we get, $x = 70 - y $

Substituting 'x' in equation 2 we get,

$70 - y + 10 = ( y + 10 )/2$

$2 (70 - y + 10 ) = ( y + 10 )$

$140 - 2y + 20 = y + 10$

Rearranging the equation we get,

$y + 2y = 140 + 20 - 10$

$3y = 160 - 10$

$3y = 150$

$y = 150/ 3$

$y = 50$

Substituting the value of 'y' in eqn 1 we get,

$x + 50 = 70$ 

$x = 70 - 50$

$x = 20 $

So, son's age is $20$ years and father's age is $50$ years.

The correct option is 2). 50 years ,20 years