A block of mass 5kg on a plane that is inclined at 30° to the horizontal, calculate the magnitude and direction of the frictional force experienced by the block

Engines for propeller-driven aircraft are limited in their maximum rotational speed by the fact that the tip speed of the propeller must not approach the speed of sound in air (mach i). taking 6 ft as a typical diameter for a propeller of a light airplane and 1100 fils as the speed of sound, find the upper limit on the rpm (revolutions per minute) of the propeller shaft.

I’ve been stuck on this for a while

What is part of a line has one endpoint and continues in one direction?