1. For motion down the incline

   Mass: $m=2\,\text{kg}$

   Inclination: $\theta=30^\circ$

   Acceleration downward along plane: $a=3\,\text{m/s}^2$

   Component of weight along plane: $mg\sin\theta = 2\cdot 10 \cdot \sin 30^\circ = 20\cdot \frac{1}{2}=10\,\text{N}$

   Since the body slides down, friction acts up the plane.

   Applying Newton's second law along the plane downward: $mg\sin\theta - f = ma$ $10 - f = 2\cdot 3 = 6$ $f=4\,\text{N}$

2. For motion up the incline with same acceleration

   Now the body is to move up the plane with acceleration $3\,\text{m/s}^2$ upward.

   Forces acting down the plane are:

   • component of weight = $10\,\text{N}$
   • friction = $4\,\text{N}$

   So total opposing force downward is: $10+4=14\,\text{N}$

   Let the required external force upward be $F$.

   Applying Newton's second law upward along plane: $F - 14 = ma = 2\cdot 3=6$ $F=20\,\text{N}$

3. Check options

   • A: $14\,\text{N}$ ❌
   • B: $20\,\text{N}$ ✅
   • C: $6\,\text{N}$ ❌
   • D: $4\,\text{N}$ ❌

Therefore, the required external force is: $\boxed{20\,\text{N}}$