Area of composite figures

First way: pretend the bite was never taken. The whole rectangle would be 19 × 19 = 361.

Then take the bite off. It is 7 × 6 = 42, so the L is 361 − 42 = 319 square cm.

Second way, and it works on any of these: cut the L into two rectangles.

The bottom strip is 19 × 13 = 247, and the piece standing on it is 12 × 6 = 72.

247 + 72 = 319 square cm — the same as the first way.