Answer:
500 seconds.
Explanation:
it drops 2 ft/sec, so it's altitude decreases 2ft every second, so the slope is negative 2. We start out at 1000ft, so that's our y intercept and we need to set y to 0, as that's the altitude when the bird lands. So in form
y = mx + b, we plug in our values:
0 = -2x + 1000
0 + 2x = -2x + 2x + 1000
2x = 1000
x = 500