Answer:
∠6=78° ∠7=102° ∠14=78°
Step-by-step explanation:
Angles 6 and 7 are supplementary angles so ∠a+∠b=180°
in this case it would be 102°+x=180° and you subtract 102° from 180° getting 78°
∠7 is the vertical angles postulate stating that any angles vertical to each other are eaqual

has gradient

which at the point (-1, 4, 3) has a value of

I'm not sure what the given direction vector is supposed to be, but my best guess is that it's intended to say
, in which case we have

Then the derivative of
at (-1, 4, 3) in the direction of
is

You have 28 meters of fence to make 3 sides.
28/3 = 9.3333
The pen will be 9.3333 by 9.3333 meters
A2+b2=c2 and get your answer