PLEASE I REALLY NEED YOUR HELP This problem is from my class

PLEASE! I REALLY NEED YOUR HELP! This problem is from my class (an advanced math class):

1. Prove that a 15 x 8 board cannot be covered by 2 L-tetrominoes and 28 skew tetrominoes.

Solution

Ttetromino square tetromino Ltetromino skew tetromino straight tetromino Color the board using the traditional chessboard coloring. Then there are 60 black squares and 60 white squares. Each T-tetromino covers either 1 or 3 black squares, therefore seven T-tetrominoes must cover an odd number of black squares. Each L-tetromino covers 2 black squares, therefore nine L-tetrominoes must cover 56 (i.e. odd and even number of ) black squares. Thus all 28 tiles together must cover an (odd + even=) odd number of black squares. However, the board has an even number (60) of black squares, therefore a covering is not possible.