Explanation:

Let's break it down:

- Let son’s present age = x years, father’s present age = y years.

- "n years back, I was as old as you are now" ? y - n = x

- "My present age is four times your age n years back" ? y = 4(x - n)

- The sum of their ages: x + y = 130

From (1): y - n = x ? n = y - x

Substitute n into (2):

y = 4(x - (y - x)) = 4(2x - y)

So, y = 8x - 4y ? 5y = 8x ? y = (8/5)x

Now use x + y = 130

x + (8/5)x = 130 ? (13/5)x = 130, x = 50, y = 80

Difference = 80 - 50 = 30 years

So, option 1 ("30 years") is correct.