Answer
Y=-1000x+25000
$ \fbox{2030}$
Work Step by Step
M=-1000
B=25000
You start out with 25000 bears so that is the y-intercept. The amount of polar bears declines by 1000 each year so the slope is -1000. Make an equation: y=-1000x+25000
Find when y equals 0:
-1000x=-25000
x=25
$ \fbox{2030}$