$$\require{cancel}$$
We shall suppose that the times given are $$0^{\text{h}} \ \text{TT}$$, and that the observations were made by an observer at the centre of Earth. In practice, an observer will report his or her observations in Universal Time, and from the surface of Earth. We shall deal with these two refinements at a later time.
The “observations” given above are actually from an ephemeris for the minor planet 2 Pallas published by the Minor Planet Center of the International Astronomical Union. They will not be expected to reproduce exactly the elements also published by the MPC, because the ephemeris positions are rounded off to $$0^\text{m} .01$$ and $$0^\prime .1$$, and of course the MPC elements are computed from all available observations, not just three. But we should be able to compute elements close to the correct ones. Observations are usually given to a precision of about $$0.1$$ arcsec. For the purposes of the illustrative calculation let us start the calculation with the right ascensions and declinations given above to six decimal places as exact.