One example of this number is 24, or maybe 12, just follow the rules and you'll have a lot of answers.
The question marked angle is equal to 138
To get better at 12's:
Write down on your paper your 1's facts in column skip 5 and 11 going to 14 (a vertical line - line that goes up and down). To the right of that column, write your two's facts 0 to 8 and repeat again. Then you will have your 12's! Should look as follows
12's:
0 0 = 12 x0
1 2 = 12 x1
2 4 = 12 x2
3 6 = 12 x3
4 8 = 12 x4
6 0 = 12 x5
7 2 = 12 x6
8 4 = 12 x7
9 6 = 12 x8
10 8 = 12 x9
12 0 = 12 x10
13 2 = 12 x 11
14 4 = 12 x 12
Keeping in mind that "dx" is the delta x, or differential over the x-axis, whilst "dy" is the delta y or differential over the y-axis,
