Final answer:
Angle 3 is equal to angle 7 because both are equal to angle 6, but without further context, we can't determine if they are supplementary, complementary, or vertical angles.
Step-by-step explanation:
If angle 3 is equal to angle 6, and angle 6 is equal to angle 7, then by the transitive property of equality which is a basic mathematical principle, we can conclude that angle 3 is equal to angle 7. This means that the measurement of angle 3 and the measurement of angle 7 are the same.
However, we do not have enough information to determine whether they are supplementary, complementary, or vertical angles based purely on the information that they are equal.