Your question is incomplete since friction will come into play here so without coefficients given its an incomplete question :)

Problem:
Two blocks of masses 2 kg and 4 kg are connected by a massless string which is just taut. Now two forces 3 N and 14 N are applied to the blocks. What is the tension in the string?

Solution:
To find the tension in the string, we need to analyze the forces acting on each block separately.

Force on the 2 kg block:
The 2 kg block is subjected to two forces - the tension in the string (T) and the applied force (3 N). According to Newton's second law of motion, the net force acting on an object is equal to the product of its mass and acceleration. Therefore, we can write the equation as:

Net force = mass * acceleration

The net force acting on the 2 kg block is the sum of the tension and the applied force, which can be written as:

T + 3 N = (mass of 2 kg block) * (acceleration of 2 kg block)

Force on the 4 kg block:
Similarly, the 4 kg block is subjected to two forces - the tension in the string (T) and the applied force (14 N). Using the same equation, we can write:

T + 14 N = (mass of 4 kg block) * (acceleration of 4 kg block)

Equating the accelerations:
Since the blocks are connected by a massless string, they will have the same acceleration. Therefore, we can set the accelerations equal to each other:

(mass of 2 kg block) * (acceleration of 2 kg block) = (mass of 4 kg block) * (acceleration of 4 kg block)

Simplifying this equation, we get:

2 kg * (T + 3 N) = 4 kg * (T + 14 N)

Finding the tension:
Now, we can solve the equation to find the tension in the string.

Expanding the equation:

2 kg * T + 6 N = 4 kg * T + 56 N

Rearranging terms:

2 kg * T - 4 kg * T = 56 N - 6 N

-2 kg * T = 50 N

Dividing both sides by -2 kg:

T = -50 N / -2 kg

T = 25 N

Therefore, the tension in the string is 25 N.