Answer:
7n = 12+ 3n
Step-by-step explanation:
The first thing to do is subtract 3n from 7n. This would get you 4n = 12. 4 times 3 equals 12, so n equals 3.
To check your answer. 21 = 12+9. sure enough it matches our answer
Answer:

Step-by-step explanation:
It is given that,
Magnitude of a A, 
magnitude of B, 
The angle betwern a and b is 
Dot product,

So, a.b is equal to 0.
Answer:
Angles 7, 2, and 6
Step-by-step explanation:
Angle 7 is congruent by corresponding angles to angle 3.
Angle 2 is congruent by vertical angles to angle 3.
Angle 6 is congruent by vertical angles to angle 7, which is congruent to angle 3, so angle 3 and angle 6 must also be congruent.