Two hot air balloons are flying above a park. One balloon started at a height of 3,000 feet above the ground and is decreasing in height at a rate of 40 feet per minute. The second balloon is rising at a rate of 50 feet per minute after beginning from a height of 1,200 feet above the ground.

To model the situation of the two hot air balloons, we define \( h \) as the height of each balloon after \( m \) minutes.

1. **For the first balloon**:
- It starts at a height of 3,000 feet.
- It is decreasing in height at a rate of 40 feet per minute.
- Therefore, the height of this balloon after \( m \) minutes can be expressed as:
\[
h = 3000 - 40m
\]

2. **For the second balloon**:
- It starts at a height of 1,200 feet.
- It is rising at a rate of 50 feet per minute.
- Therefore, the height of this balloon after \( m \) minutes can be expressed as:
\[
h = 1200 + 50m
\]

Putting these two equations together, we find that the system of equations representing the situation is:
\[
h = 3000 - 40m
\]
\[
h = 1200 + 50m
\]

Now we can compare this system with the given options:

- **Option : \( m = 3,000 - 40h \), \( m = 1,200 + 50h \)
- **Option B**: \( h = 3,000 - 40m \), \( h = 1,200 + 50m \) (matches our equations)
- **Option C**: \( h = 3,000 + 40m \), \( h = 1,200 - 50m \)
- **Option D**: \( h = 3,000m - 40 \), \( h = 1,200m + 50 \)

Thus, the correct answer is **Option B**:
\[
h = 3,000 - 40m
\]
\[
h = 1,200 + 50m
\]