Dawb

A pendulum is constructed from a thin, rigid, and uniform rod with a small sphere attached to the end opposite the pivot. This arrangement is a good approximation to a simple pendulum (period = 5.97 s), because the mass of the sphere (lead) is much greate...

21/4=5.25 ft each

The period is the same. If you do a proof with different equations, the mass of an object doesn't change its period. However, if the length of the spring was changed the period then would change.

When you do the proof, the mass ends up canceling out of the equation so it can be ignored.

12 inches in a foot. 12/4=3 inches

Pick whether you like to work with fractions or decimals better. Convert all of the numbers to be all fractions or all decimals (whichever one you prefer will work).