Let's use algebra to solve this problem. Let K represent Koushik's current age, and T represent Tahmid's current age. We'll set up equations based on the given information.

"Tahmid is four times as old as Koushik": T = 4K

"In x years, Tahmid will be three times as old as Koushik": In x years, Tahmid's age will be T + x, and Koushik's age will be K + x. So, we can write: T + x = 3(K + x)

Now, we have a system of two equations:

T = 4K
T + x = 3(K + x)
We can solve this system of equations to find Koushik's age (K) in terms of x.

First, substitute the value of T from the first equation into the second equation:

4K + x = 3(K + x)

Now, let's solve for K:

4K + x = 3K + 3x

Subtract 3K and x from both sides:

4K - 3K = 3x - x

K = 2x

So, Koushik's current age, in terms of x, is 2x.