After 18 years, Swarnim will be 4 times as

6 years

Let Swarnim's present age be $x$ yr.

After $18 \mathrm{yr}$, Swarnim's age $=(x+18) \mathrm{yr}$

According to the question,

$x+18=4 x$

$\Rightarrow \quad x-4 x=-18 \quad$ [transposing $4 x$ to LHS and 18 to RHS]

$\Rightarrow \quad-3 x=-18$

$\Rightarrow \quad \frac{-3 x}{-3}=\frac{-18}{3}$

$\Rightarrow \quad \frac{-3 x}{-3}=\frac{-18}{3} \quad$ [dividing both sides by $-3$ ]

$\therefore \quad x=6$

Hence, Swarnim's present age is $6 \mathrm{yr}$.