Let $n$ be a natural number. Find all solutions $x$ of the system of equations $$\left\{\begin{matrix} sinx+cosx=\frac{\sqrt{n}}{2}\\tg\frac{x}{2}=\frac{\sqrt{n}-2}{3}\end{matrix}\right.$$ On interval $\left[0,\frac{\pi}{4}\right).$
1. **Analyze the given system of equations:**
   \[
   \left\{
   \begin{matrix}
   \sin x + \cos x = \frac{\sqrt{n}}{2} \\
   \tan \frac{x}{2} = \frac{\sqrt{n} - 2}{3}
   \end{matrix}
   \right.
   \]
   We need to find all solutions \( x \) in the interval \(\left[0, \frac{\pi}{4}\right)\).

2. **Square the first equation:**
   \[
   (\sin x + \cos x)^2 = \left(\frac{\sqrt{n}}{2}\right)^2
   \]
   \[
   \sin^2 x + \cos^2 x + 2 \sin x \cos x = \frac{n}{4}
   \]
   Using the Pythagorean identity \(\sin^2 x + \cos^2 x = 1\), we get:
   \[
   1 + 2 \sin x \cos x = \frac{n}{4}
   \]
   \[
   2 \sin x \cos x = \frac{n}{4} - 1
   \]
   \[
   \sin 2x = \frac{n - 4}{8}
   \]

3. **Express \(\tan \frac{x}{2}\) in terms of \(\cos x\):**
   \[
   \tan \frac{x}{2} = \sqrt{\frac{1 - \cos x}{1 + \cos x}}
   \]
   Given:
   \[
   \tan \frac{x}{2} = \frac{\sqrt{n} - 2}{3}
   \]
   Equate the two expressions:
   \[
   \sqrt{\frac{1 - \cos x}{1 + \cos x}} = \frac{\sqrt{n} - 2}{3}
   \]
   Square both sides:
   \[
   \frac{1 - \cos x}{1 + \cos x} = \left(\frac{\sqrt{n} - 2}{3}\right)^2
   \]
   \[
   \frac{1 - \cos x}{1 + \cos x} = \frac{(\sqrt{n} - 2)^2}{9}
   \]

4. **Solve for \(\cos x\):**
   Let \( k = \frac{(\sqrt{n} - 2)^2}{9} \):
   \[
   1 - \cos x = k (1 + \cos x)
   \]
   \[
   1 - \cos x = k + k \cos x
   \]
   \[
   1 - k = \cos x (1 + k)
   \]
   \[
   \cos x = \frac{1 - k}{1 + k}
   \]

5. **Substitute \(\cos x\) back into the equation for \(\sin 2x\):**
   \[
   \sin 2x = \frac{n - 4}{8}
   \]
   \[
   \sin 2x = 2 \sin x \cos x
   \]
   Using \(\cos x = \frac{1 - k}{1 + k}\):
   \[
   \sin x = \sqrt{1 - \cos^2 x} = \sqrt{1 - \left(\frac{1 - k}{1 + k}\right)^2}
   \]
   \[
   \sin x = \sqrt{\frac{4k}{(1 + k)^2}}
   \]
   \[
   \sin x = \frac{2\sqrt{k}}{1 + k}
   \]

6. **Check the range of \( n \):**
   Given \( 4 \leq n \leq 7 \), we need to check which values satisfy both equations.

7. **Verify solutions for \( n = 4 \) and \( n = 7 \):**
   - For \( n = 4 \):
     \[
     \sin 2x = \frac{4 - 4}{8} = 0 \implies 2x = 0 \implies x = 0
     \]
     \[
     \tan \frac{0}{2} = 0 = \frac{\sqrt{4} - 2}{3} = 0
     \]
     Thus, \( (x, n) = (0, 4) \) is a solution.

   - For \( n = 7 \):
     \[
     \sin 2x = \frac{7 - 4}{8} = \frac{3}{8}
     \]
     \[
     2x = \arcsin \frac{3}{8} \implies x = \frac{\arcsin \frac{3}{8}}{2}
     \]
     \[
     \tan \frac{x}{2} = \frac{\sqrt{7} - 2}{3}
     \]
     Thus, \( (x, n) = \left(\frac{\arcsin \frac{3}{8}}{2}, 7\right) \) is a solution.

The final answer is \( \boxed{ (x, n) = (0, 4) } \) and \(\left(\frac{\arcsin \frac{3}{8}}{2}, 7\right)\).