The main purpose of the turbine in the turbojet engine is to
a. compress the air.
b. reduce the temperature of the exhaust gas.
c. increase the velocity of the exhaust gases.
d. drive the compressor.

The best answer is D.

The engine sucks in air at the front. A compressor  squeezes the air.  The compressed air is sprayed with fuel and an electric spark lights the mixture. The burning gases expand and blast through  the nozzle at the back of the engine. As the hot air is going through the nozzle, it passes through another set of blades called the turbine. The turbine is attached to the same shaft as the compressor. As the turbine spins, it also spins the compressor.

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