13/21 * (9/26 - 2 3/13) - (-2/3)³ = - 47/54,
1) 9/26 - 2 3/13 = 9/26 - 29/13 = 9/26 - 58/26 = - 49/26 = -1 23/26,
2) 13/21 * (-1 23/26) = -13/21 * 49/26 = -7/6 = - 1 1/6,
3) (-2/3)³ = -8/27,
4) - 1 1/6 - (-8/27) = -7/6 + 8/27 = -63/54 + 16/54 = - 47/54.