Complex sentence: Whereas Sudoku has the additional constraint of 3x3 "boxes", in Str8ts rows and columns are divided by additional clues are set in some of the black cells--these numbers remove that digit as an option in the row and column.
Split into simpler sentences: Whereas Sudoku has the additional constraint of 3x3 "boxes", in Str8ts rows and columns are divided by blacks cells. Additional clues are set in some of the black cells--these numbers remove that digit as an option in the row and column.