What number goes in the missing space?

20 goes in the missing space.

In each example, the number in the top right equals the number in the top left times 2.

4*2=8
6*12=12
10*2=20

Find the pattern. 
The numbers are doubled: 8*2=16 16*2=32
Therefore the number in the missing spot would be 10*2 or 40/2
which equals 20.

Hope this helps!