In some organisms karyokinesis is not followed by cytokinesis…

(a) Nuclei and cells. Each round doubles the number of nuclei: $2^{8} = 256$ nuclei. With no cytokinesis the cytoplasm never divides, so all of them lie in $1$ multinucleate cell, a syncytium. The liquid endosperm of coconut forms this way.

(b) Chromosomes. Mitosis is an equational division, so every nucleus has $24$ chromosomes: $256 \times 24 = 6144$ chromosomes.

(c) Nuclear divisions. Each division of a nucleus adds one nucleus. Going from $1$ to $256$ nuclei takes $256 - 1 = 255$ divisions.