Answer:
Okay just by looking at it the numbers go up By times 2
1). 10*2=20
2). 20*2=40
3). 40 *2=80
4). 80*2= 160
5). 160*2=320
6). 320*2=640
7). 640*2=1,280
8). 1,280*2=2,560
9). 2,560*2=5,120
10). 5,120*2=10,240
11). 10,240*2=20,480
But as we see every other number is negative
-10 20 -40 80 -160 320 -640 1,280 -2,560 5120 -10,240 20,480
20,480 is your answer!