Variant 7.8.3. The cells of a $30 \times 30$ table are colored in $n$ colors such that for any cell, the union of its row and column contains cells of all $n$ colors. Find the maximum possible number of blue cells if

(a) $(1$ point) $n=2$;

(b) $(3$ points) $n=15$.
Answer: (a) 870. (b) 480.