How in gods name do you do this i’m confusion

The easiest way to go about problems like these is to divide the complex shape into simpler shapes.

for instance, you could imagine the 20x9 and 4x20 rectangles separate from the 9x7 section in the middle.

it would be 9x7 because 9+4+x = 22 and 11++y+2 = 20

Ibelieve 4mn because it’s like you’re combining them