You know the horizontal line is 180°. If the left side of the horizontal line is 90° (right angle), then the right side of the horizontal line should be 90° too. (180° - 90° = 90°)
The probability is 3/14. There are 2 multiples of 4 in 14, which is 8 and 12. There is only 1 multiple of 6 in 14 which is 12. 1+2=3. It is possible outcomes over total outcomes so 3/14.