To convert \( 364 \, \text{m}^2 \, 789 \, \text{mm}^2 \) to \(\text{cm}^2\):

1. **Convert square meters to square centimeters**:
\[
1 \, \text{m}^2 = 10,000 \, \text{cm}^2
\]
\[
364 \, \text{m}^2 = 364 \times 10,000 = 3,640,000 \, \text{cm}^2
\]

2. **Convert square millimeters to square centimeters**:
\[
1 \, \text{mm}^2 = 0.01 \, \text{cm}^2
\]
\[
789 \, \text{mm}^2 = 789 \times 0.01 = 7.89 \, \text{cm}^2
\]

3. **Add both converted values**:
\[
3,640,000 \, \text{cm}^2 + 7.89 \, \text{cm}^2 = 3,640,007.89 \, \text{cm}^2
\]

So, \( 364 \, \text{m}^2 \, 789 \, \text{mm}^2 = 3,640,007.89 \, \text{cm}^2 \).

### For the second part: \( 201 \, \text{ha} \, 345 \, \text{m}^2 \) to \(\text{dm}^2\)

1. **Convert hectares to square meters**:
\[
1 \, \text{ha} = 10,000 \, \text{m}^2
\]
\[
201 \, \text{ha} = 201 \times 10,000 = 2,010,000 \, \text{m}^2
\]

2. **Now add the \( 345 \, \text{m}^2 \)**:
\[
2,010,000 \, \text{m}^2 + 345 \, \text{m}^2 = 2,010,345 \, \text{m}^2
\]

3. **Convert to square decimeters**:
\[
1 \, \text{m}^2 = 100 \, \text{dm}^2
\]
\[
2,010,345 \, \text{m}^2 = 2,010,345 \times 100 = 201,034,500 \, \text{dm}^2
\]

So, \( 201 \, \text{ha} \, 345 \, \text{m}^2 = 201,034,500 \, \text{dm}^2 \).