1. Given data

   • Weight at Earth's surface: $W = 18\,\text{N}$
   • Altitude above surface: $h = 3200\,\text{km}$
   • Radius of Earth: $R = 6400\,\text{km}$

2. Formula for weight at altitude

   Weight varies inversely as the square of distance from the center of Earth:

   $W_h = W \left(\frac{R}{R+h}\right)^2$

3. Substitute the values

   $R+h = 6400 + 3200 = 9600\,\text{km}$

   So,

   $W_h = 18\left(\frac{6400}{9600}\right)^2$

4. Simplify the fraction

   $\frac{6400}{9600} = \frac{2}{3}$

   Therefore,

   $W_h = 18\left(\frac{2}{3}\right)^2 = 18\cdot \frac{4}{9}$

5. Calculate

   $W_h = 18 \times \frac{4}{9} = 2 \times 4 = 8\,\text{N}$

6. Check options

   • A: $9.8\,\text{N}$ ❌
   • B: $4.9\,\text{N}$ ❌
   • C: $19.6\,\text{N}$ ❌
   • D: $8\,\text{N}$ ✅

Hence, the correct answer is D.