Electric signs and metal equipment of outline lighting systems, other than the portable and double-insulated types, shall be grounded by connecting them to the ? of the supplying branch circuit or feeder.

Equipment grounding conductor.

Explanation:

EGC ( Equipment grounding conductor) is used to ground the non current carrying metal parts of equipment. It provides a safe path for the flow of ground fault current by keeping the equipment close to the ground potential. It can be apply in the above mentioned case for grounding electric signs and metal equipment of outline lighting system. So we can say that Electric signs and metal equipment of outline lighting systems, other than the portable and double-insulated types, shall be grounded by connecting them to the Equipment grounding conductor of the supplying branch circuit or feeder.

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west