Answer:
b-d
Step-by-step explanation:
At the airport, d airplanes flew away, and b were still there.
We are required to determine how many more airplanes stayed at the airport than flew away.
To do this, we subtract the number of airplanes which flew away from the number which stayed.
Therefore:
Number of more airplanes which stayed than flew away
=Number of airplanes which stayed-Number of airplanes which flew away
= b-d
