help me with this step by step

Answer:
C
Step-by-step explanation:
Elevation of the plane is y.
y =
The airplane starts at an elevation of 8500 feet
y = 8500
It is said that the plane loses elevation at a rate of 150 feet per minute.
y = 8500 - 150
We don't know how many minutes the plane has been losing elevation so we use m
y = 8500 - 150m