Ariana is bowling with her friends. Her bowling ball has a radius
4.1
inches long. After she releases the ball, it's possible to track the height of the finger hole above the ground. When the ball touches the ground, the finger hole is at the
12
-o'clock position. As the ball moves down the lane, it has backspin and thus rotates counter-clockwise based on the given diagram.

A woman releases a bowling ball moving left to right. As the ball moves to the right, it rotates counterclockwise due to backspin.

Complete the definition for function
f
that represents the finger hole's height above the ground (in inches) in terms of the number of radians
a
the ball has rotated since it touched the ground. (Note that
a
is a number of radians swept out from the
12
-o'clock position.)