(a) The board shall adopt the plan of taxation which will, in its judgment under the evidence, be most conducive to the equitable distribution of the district's tax.(b) If the plan adopted by the board is made under the provisions of Section 51.512 of this code, the order shall specify the proportion of the tax which falls under each designated classification.(c) The order of the board is final and cannot be reviewed or questioned in any court except on the ground of fraud or palpable and arbitrary abuse of discretion. Acts 1971, 62nd Leg., p. 350, ch. 58, Sec. 1, eff. 8/30/1971.